I am bring billed but my contract has been blocked. No access to internet yet uncapped data line

Hi. From 2 weeks after receiving a call from an mtn agent to upgrade my contract which I refused my data line has been blocked. I have logged on queries but no gives me proper answers. To my knowledge my contract is uncapped... After 3gb of data used line will be a bit slow. But not cut off. Dey don't seem to understand the meaning of uncapped. After 6days dey have blocked my line. I have people who have this contract and don't have a problem. I only started having dis problems after the call. Which I am not sure what the agent has done. I'm being billed for a contract and I'm not being able to use it. This is a total breach of contract form mtn side. I have had this contract for over 4 years and I have 3 more contract with them. Please assist me. ********** 558 ********** Thank you