Bad service

Auto and General is very quick to collect premiums, they promise you heaven and earth when it comes to you cover. however, when i try to claim for a windscreen replacement, they looked for the cheapest replacement windscreen they can find, forgeting that by doing this the warranty of my vehicle will be affected. i explained this to them but for them to consider what I'm saying to them, they requesting a letter (i have to go get a motivation letter from the vehicles manufacturer) then the'll make a decision based on this. Why am i the one who have to go the extra mile for this? isn't it their job to make sure that I get nothing but the right quality and servie first time? I made a very big mistake for switching ...