MTN complaint

I have a data contract with MTN which I signed up for in November 2020 via their Black Friday promotions. I was told that to cancel after two years (which is now), I have to give one month's notice by phoning 135. This I started doing on the 11th October, however when I got through to cancellations I was put on hold up to 30 minutes at a time, listening to the same ads over and over. I tried this 135 number for days and no human being ever answered. I then sent an email to customer care and was advised to email the "retentions " department. I have sent numerous emails with the reference number I was given but to no avail. I have again been debited for the data contract which I do not want anymore. I think that the service from MTN is absolutely shocking. I am at my wit's end trying to contact them. Please help.