overcharging

i have been a sprint costumer for many years. i will admit i had a returned check and i paid that bill with cash the day i found out it had been returned. after that sprint pcs turned my services off and would not re connect them. i had 4 lines of service with them and after THEY turned off my service for the returned check (which the account was paid in full with cash) i recieved a bill of over $1,100 for early termination fees. first of all i did not cancel my contract they did. i never signed anything stating that if they cancel they can charge me those fees. the contract states that if i cancel they will be charged. so now it his been turned over to a slime ball collection company and going to hit my credit. does sprint think they can just make things up in there so called signed contracts after the fact. it is not my problem that they cancelled by service so i should not have to pay the early termination fees.