Received PCN Reminder after appeal but no POPLA

I received a PCN from Met Parking Services (BPA member) on 7th April 2017. I read the newbie forum and appealed online (as recommended) on their website. I did screenshot and the reference number. It said they will respond in 10 days. I waited for 3 weeks and I received nothing. I was very happy that everything is done.

However, I received a PCN reminder today (2 months later) saying amount due, with seemingly the standard 'further action will be taken... solicitors/debt recovery..'. It also said '.. the independent appeals service (POPLA) is no longer available..'

My question is, should I response?
If yes, should I do it online or post?
If yes, what I should write? Do I write with my screenshot and reference number, saying that "..I have submitted my appeal online and you didn't response within 10 days and too bad for you, and don't write to me again.." ?

Or if there are already thread that have this advise that I've missed, please let me know.

I've searched around, and I can't find similar case to mind.

//-- Added summary of my story and what I've done for other to refer to

I am a regular McD customers due to our kids. And that particular night, I've sent the grannies onto the planes, it was late, the kids are bored (with the walking, and queue-ing in the airport), I thought it was nice for them to play a bit at the McD with the happy meals, drawing, and tablets on the table. I am such a regular McD person that I've calculated that I can never exceed the parting time limit. I was so wrong because this particular McD has a 60 min period as oppose to the 90 min period that I've used to.

I've then got a PCN from MET Parking Services. I searched around and it seems that many have actually talk to the manager in person to get the PCN cancelled. I wasn't going to drive all the way to the airport, especially with kids, it's not the way you want to spend your weekend. I gooogled the restaurant contact, and called for the manager. The manage answered the call, I tell her the story. She said there is nothing she can do at the moment, and she said that I have to make an appeal to obtain a number before she can get the PCN cancelled. I assume she meant the POPLA code. I obtained her name, and couldn't be borther contacting her back again. I suspect at the time of day of my call (Friday, 8pm+) may have got on hold of a less experience manager, or as many other posts describe, you may need to be in person and make a fuss before they will do anything.

Then I did my appeal online on the MET webpage (fairly standard first appeal, based on the newbie thread). I did a lot of work doing my appeal, I have it drafted, reviewed, added customised appeal reasons (eg not copied pasted). I was hoping that the first appeal letter would make them not to even send me the POPLA. On hind sight, I think it probably doesn't really matter, they are going to reject it with a standard reject letter anyway.

First, I've entered the details and only get a reference number at the end (eg no summary of what I've said or entered). Common sense tells me that feels odd. So, I did another appeal again, screenshot of what I've entered and again the new reference number. I would advise you to do the same, in case they came up with the reason that you've entered the wrong information and you have no proof or can't recall of what you did.

Then, 3 weeks passed, I received nothing. Then this happen. Story continue on this thread.