Mtn south Africa, advertise 60 GB but give clients 5gb instead of 60 GB

Good day, I took a new contract on Mtn on the 29th April 2020. The contract was for Sim only, 20 GB all day and 40 GB night for 24 months. On the 29th April Mtn sent me a prorated data of 1,33 GB for 1 week. I called Mtn to retricfy their mistakes, no one helped me. They said it was a promotion and it's called 5 GB data. When I took a contract I told them I want 60 GB and they agreed and I agreed to the terms over the phone. Now Mtn is not honoring the terms of the contract. I called this morning and I want to cancel the contract, I've been taking to the pillar to post. Mtn is robbing me. I want what is due to me, not 5 GB. I want 60 GB. I used my airtime to call their service provider, of which I was not helped. I went to the Mtn outlet store yesterday, and they said that they cannot help me. Imagine the stress this company is causing me. Please expose them. I logged several calls, they didn't even bother to call me and follow up on my query.