MTN RETENTION DEPARTMENT PATHETIC

I want to cancel my contract. One has to phone 135 and transfer to retentions department. I have phoned them everyday the past week and held for up to 30mins at times - THEY DON’T ANSWER. I then spoke to normal customer care and told them I’m not getting through - she wanted to transfer me to them. After I refused and asked for an email address to contact them on, she said I must send a mail to ***, BUT THEIR MAILBOX IS FULL!!!!!!

How do I cancel then??? Absolute disgrace!