Beyond annoyed

I took a contract with u guys 2 years back and i made sure i payed it up in full with no issues ...i called around the end of November 2017 to cancel both my contracts so that the last installment will be in Dec ...little did i know that in January they will debit again i have been calling and calling the call center so that this debit order doesnt go off and for them to explain y they havent stopped debiting....everyone is aware how difficult January is and i hate that i have to pay for a contract that i have completed.....plz fix this ASAP as i am beyond irate and when u call me do not ask me about stupid reff numbers