Repaired one thing and damaged something else!!

I recently had a crack on my camera lense repaired and aince getting the phone back, the back button has been giving me problems and now has stopped responding completely. I went to MTN and based on the fact the phone was opened by the cellphone insurer MTN does not want to take the phone to jave a look at it. So basically the insurance directly effects the manufacturer warranty? I really dont have the time to deal with this insurance coz my last experience was horrible. 24hour mobility please contact me to cancel this bogus insurance.