ABSA, MTN'S PARTNER IN CRIME

I am an ABSA customer since forever but I cannot get them to assist in preventing MTN from *****ing money off my account.

My contract ended last year and I showed ABSA proof that I had asked MTN to end the contract and switch to Pay-as-you-go. Instead MTN stopped charging me R169 and is now charging me R539 for the 2nd month in a row!!! Why would ABSA not assist me in ending this.