Cancel Post Office Broadband & phone

Signed a 18months contract in Feb 17 for broadband and phone , and since then I’ve had very slow internet that most days my phone goes onto 4G and my Smart TV does not work. I’ve called post office numerous times and each time spending an average of an hour on the phone and they do tests and tell me my line speed was increased and should be fine, I’d call back after a month as still not working well.
As of Nov 2 I spent an hour on the phone with technical and doing tests which resulted in me having no internet at all as they found a fault and was told it would be fixed in 72hr. The following week I called and was told a new router was on its way. After speaking about cancel options and told i would be compensated for non service and to allow them time to fix it or could cancel without penalty, which I agreed to i still have very slow service and Today, post office tell me they will not allow me to cancel as they increased the speed to 8mp but it’s still slow on my end and I’m tied also in unless I complete 3 speed checks on .supportal-test.co.uk using a computer as it doesn’t not support Apple! We don’t own a computer and i just want out the contract.
Is there any possibility?