The Letting Corp - know for not paying your deposit back

My sister and I have rented a apartment with the letting corp for 2 years. When we moved in the place was filthy and the paint job was terrible. We complained about this and the Letting Corp sent a painter who did an even worse job on the paint. The walls where practically see through it was awful. We also cleaned the place out ourselves. Now that we moved out they will not pay our deposit back adding bogus amounts we have to pay for admin fees etc. They are grasping at straws and after we signed the amount to be released they will still not pay us our deposit back. I WILL NEVER SUGGEST ANYONE RENT FROM THEM. PREVIOUS TENANTS COMPLAIN of the exact same thing.