Bad customer service

Having a Jet account for many years and always paying it on time. I am currently in arrears for a payment in August that somehow cannot be picked up. I have sent proof of payment on more than one occasion and it is ridiculous that you have to keep explaining yourself to numerous callers that all say they will resolve this. I am now being charged collection fees for outstanding account I will probably end up paying twice as much for the missed payment thanks to their incompetence. No one seems to know how to resolve this. Extreme bad service.