Jitter / Line Quality - Gaming performance issue - upgraded 3 times still awful!

Hi, I'd switched to simply broadband a little while back from Sky and my net loading speed and gaming performance has drasticly dropped! I've rang up numerous times, I was supposed to recieve technician phone calls 3+ times at certain time slots (Which they either rang hours later when I was busy/unable to take the call or not at all). I'd upgraded to fibre medium hoping this would fix the performance and it made it slightly very slightly better but still awful and delayed,

I'm now on Fibre Large which is again very slightly better but at times unplayable! I've done numerous tests with the likes of BT and sky and they say the speeds i'm able to get minimum are over 50meg download - why then am i getting 35 download? and 10 meg upload? surely this has something to do with a cap and the way talk talk run their network. I'm seriously frustrated, games are unplayble with the jitter / lag (bufferbloat maybe?) It's not as if i'm the first to complain about this so the issue is obviously with talk talk somewhere.

Seemingly when I complain the issue gets slightly better for a week or so then back to 56k quality! I'm fine with the speed download i get but seriously what's up with the quality / jitter and drops on talk talk!? 

Thanks in Advance
Terence