MTN preying on poor

I am being victimised and being frustrated by MTN. I had a month to month contract with MTN, I have returned both sim carfd and the router on 11th of March 2025 where I was provided with reff number confirming that I did return their equipment,mind you I had already been debited for that same month(March 2025),to my suprise, end of March 2025 got debited(this time for April 2025 eventhough I have cancelled the contract)...I called MTN and I was promised that the will refund it, while waiting for refund,end of April 2025 got debited again, I called MTN and I was send from pillar tonpost on several occasions and even sent emails, still no help, MTN have now and sent me statement and invoice and threatening me legaly. I need help.