October cancelation of contract that hasn't done, even now

I had contract with mtn, it Ended on oct, but the still billing for 20gb that the allocate everymonth, i have being call since October 2024 for them to cancel the contract, even now, it has being done, only to find out the is some who did *****, with my information, and i send affidavit and my copy foe for that matter, yesterday i went to mtn the saying am owing R1000.19, which includes the simcard that is being used by the person o dont know, now i hve pay them R700 yesterday and told me to cancel the contract sametime, the say thw will today when call the saying i have to wait because the guy (Lindokuhle Mthembu) who was helping me, order for 27 of nextmonth, meaning, the contract is not canceled the are going to allocate the data and bill me, for contract that i have canceled in time, at mtn the said Lindokuhle Mthembu will call me to find the mess, i never received any call till now, Mtn service is very bad i wont refer person,