MTN gave my contract number to someone else

I took a contract with MTN in 2021 for data only sim card. I was paying around R300 before annual increase. Everything was going well until they debited y account R1630 in April which i reversed. I paid the usual debit order via EFT. I enquired and they told me that i requested data and airtime which i never did. Bear in mind that i have another number which is my main number, i was using the contract sim for data. I suspected that someone was using my number, then i logged into my Capitec app and pretend like i wanted to pay a beneficiary with the number in question. To my suprise the number was registered under someone else's names. I gave evidence to MTN ***** department who said that they will investigate, until this day there is no update. Im receiving SMSes everyday stating that i must pay. The contract expired early May, they said i cant cancel cause i have outstanding balance. Im stuck with the expired contact which i dont even need.