Contract upgraded without permission

As a unhappy customer of mtn my contract which was old run out of contract in May but only to find out it was upgraded and I was wondering how when I never agreed even when the customer agent called for the upgrade I refused that Mondo plz fix this situation my contract was upgraded on 24th May without my permission and made no agreement of that and I been trying to get hold of this problem and my bills keeps increasing please help it’s a big problem and I don’t want anything considering a charge fee I want this fixed immediately