MTN SIM card cancellation

I'm not happy I cancelled SIM card contract last September 2026 until to date MTN says I owe them. I sent customers care complaints I don't get assistance. I went to MTN shop @ Evaton mall September 2026 the agent told me contract is cancelled. I don't have SIM cards anymore because she told me I am going to forfeit those Mtn numbers.The money keep going up month in month