No MTN Service championship in the call center!

My device contract ended in june, I've been calling their contact centers for cancellations, since June til this day it has not been cancelled, every 25th they bill me, I pay, but still they manage to deactivate my cell number whereas I put a request for my two year contract to be cancelled but no one helps me whatsoever...every time I call,my call is picked up after 50 to 60min for the next available agent...I am billed every month of ofwhich my contract ended 30th June, I have never received any follow up as confirmation that it has been cancelled.