Billing for something that doesnt exist

Mtn has been trying to bill me for a 25th month on a 24 month contract. Calling the call center is useless as they give some bull**** explanation of a cancellation policy. My contract ended in september Why are you trying to bill me for october? Further to that I logged the cancellation request in September which you then only processed at the end of october Looks like they pass on their slow responses to their customers or its just plain shady business practices