Need advice re ESA being terminated

HI
I was hoping someone could offer some advice regarding my ESA being terminated.
I first claimed last August after giving up work following months of illness. At the time, I was undergoing investigations for cancer and this was the medical reason taken for ESA purposes (also the reason on my ESA statement)
My GP was originally issuing fit notes for "Stress-awaiting investigations/tests.Some weeks later, the wording changed to "stress", then again to "depression". During the cancer investigations for myself, my sister was diagnosed with cancer and died within 4 weeks and then my friend died from cancer and I became extremely depressed.
The date of my first Medical Assessment was looming and I had been offered an emergency dental appointment for the same date (two days later) I called up the Health Assessment people and asked if it would be possible to change the date. I was given a new date, no other information was provided. ie I was not told that only two dates are offered, had I known, I would have requested the dental appointment on a different date. The date of the second assessment came around (29th /11 ) and I had fallen ill with measles like symptoms.Advice from NHS 111 was to try not to be in contact with other people. I again called the Health Advisory people and asked their advice. They said they could not advise me either way but stated I would not be offered another appointment as they could only offer two. I asked if my benefit would be cancelled and the guy said no, we will send out a form for you to give your reasons in the first instance. I duly received, completed, and sent this back in early December.(4th) reiterating the reasons for not attending the medical and stating i was more than willing to attend for a medical. I heard nothing more until 19th January when I received a letter from DWP stating because I had not attended the medical on 29/11/17, they were declaring me fit for work from 30/11/17 and would be claiming back overpaid benefits.
I immediately requested a mandatory reconsideration (19/1) but received the letter today stating that they would not change their decision. Baffling to note that they state I requested the Mandatory Reconsideration on January 14th, 5 days before I was even aware of the termination of my ESA.
My questions /advice needed resolve around the following,
1. Can termination of ESA be effectively "backdated", in this case, 8 weeks, ie, I did not attend the ESA medical on 29/11, received and returned the reason why form on 4th December, DWP made their decision to terminate ESA on 11th January and letter was received on 19th January, thereby prohibiting me from making a claim for either ESA or JSA in that 8 week period, or should it only be terminated from the date of their decision ?
2. What constitutes the original medical condition for claiming ESA, the ESA statement ie under investigations for cancer, or the reasons given on my GP's sicknote ? Does the fact I am now signed off for depression and not being under investigation for cancer allow me to make a new claim for ESA ? DWP have had all the sick notes issued without delay and the woman I first spoke to at DWP, on the day I received termination letter, confirmed that they "knew" i was ill and that they had a fit note from my GP to 18th Feb confirming it.
The reason I ask this is because in the MR notice, they make a point of saying "on 9/1 a decision maker decided that you had not provided any medical evidence of this condition. Your medical evidence was for stress until 18/12/17 and the new evidence provided showed you had incapacity of Depression.
As a result, your award for ESA was disallowed from 30/11/17.
(again, conflicting dates, main paragraph states on 11/1/18 decision was made, yet later in letter it states 9/1...same as wrong dates noted for my MR request.....and the reason for not attending the appointment was not the reason why my GP has declared me unfit for work)
So, in deciding if it is a new condition, do they take the information from sick notes or from the original ESA statement ?
I intend to appeal to Tribunal, if for no other reason than to dispute that the termination should not be backdated as it would leave me with a huge overpayment through no fault of my own and has prevented me from claiming any other benefit during that period.

Finally, the only information I could find regarding termination of esa was that in considering whether or not to suspend or terminate a benefit, the Decision Maker must take into consideration if hardship will be caused and if so, the benefit must not be terminated. This was in some legislation dated back in 2010 and wondered if anyone could advise if this is still a requirement ? Being as my only other income is Housing Benefit, of course it has placed me in hardship. I refuse to claim JSA when I am still under my GP and covered until 18th February by his fit note, so I am having to sell possessions to pay for my electricity meter, nothing else is getting paid. Will the Tribunal take into account the fact that terminating my benefit and being placed in hardship was obviously not considered ?
I was offered no advise from DWP when originally calling on receipt of termination letter, only that I should claim JSA, which i refuse to do. I was also told that I could only make a MR in writing, something else which i have found to be incorrect, although I would have sent it in writing anyway as wouldn't trust any Government Department as far as I could throw them.
Sorry for this being long winded, I just wanted to give as much info as possible for a quick response.