Worse after sale service

I bought an ipad8 and have been having sound issues on it when using some apps. Returned it and they replaced it with a new one and funnily the new ones having the same problem and when i returned the new one they say all is fine and there are no issues although there is clear problems on it. On checking on apple community , i saw many ipad 8 have the same problems and this points out to a manufacturers issue. But incredible connection washes their hand off it and say they cant do anything since the supplier says no fault and are unwilling to assist furtherz