new phone contract renewal

I took out a new contract on 11 January 2021 at MTN Northgate as my old contract was about to expire. The same amount of the old contract keeps going off my account each month. I was there in person twice, first time I was told it is just pro rata - will switch to new amount soon. Second time in June I was told new contract to kick in July. Did not happen. It is 8 months later as my new contract which is less than previous contract , did not kick in. Please MTN help me to switch over to my new contract.