mtn confirmed that they will never refund me my credit amount

i logged a complain for MTN not canceling my contract in time,in closure of my account with mtn i had a credit amount of R50 of which i requested them to refund airtime not money,it was confirmed with with alice van der merwe that i will receive airtime for a credit amount.i called MTN 808 call center for the last 7 weeks with no outcome,i spoke to managers and team leaders and still awaiting them to call me back .today i decided to call MTN again just to get feedback -and i was advised that i will not be refunded due to that i used MTN internet and now i owe them R35 for November invoice,i spoke to MTN every week for my airtime only today am owing mtn.i was a loyal consumers who paid off four contracts with mtn without missing one payment or being called for no payments and if is the way MTN treat and thanks for using their network.i refer to call the managers at mtn that am gonna take a phone and i will not be expecting a call for payments as i will not pay ..you all can keep that R50 if will not refund me and i will ensure that everyone knows about it and iyou can block my number ....**** mtn 060 52 99773