CHARGED FOR AN EXPIRED CONTRACT

I previously was invited around august / September last year for an upgrade with mtn, I went to Heidelberg branch and told the manager that i didn't want a data phone anymore but wanted a cellphone. and was advised by the manager I couldn't upgrade because my work permit would be expiring soon, i advised them that i would be back for an upgrade once the permit is renewed and didn't want the account to be debited any further since i was not using it anymore. This year in January i renewed my permit and went back to the same store for an upgrade and was advised that they had to verify the permit but the manager Tshepiso would call me bek, i didn't receive her call so i phoned her 2 weeks back and was advised that she was waiting but would call me back in 2 days and up to now i have not received any call from her. they further advised that my account was with legal and i inquired why was it with legal when my contract had expired and didn't want it anymore and my contract had expired but they said they didn't know. i got hold of mtn today after many attempts and was told that it was not cancelled. im really shocked for being debited for services i did not receive