Contract Cancellation dead end!!!

I have been trying to cancel my MTN cellphone contract for the past three to four weeks. I have called the 135 number relentlessly and at different hours of the day but have not been put through to a consultant. I have gone instore, they just take my phone and call the same number with noone at the other end. I almost feel that this is a deliberate means to stop customers from trying to cancel their contracts. im tired of phoning and being on hold for close to 30 minutes . Who can assist me . The consultants instore cant help either .