Contract Upgrade nightmare

Upgraded (downgrade) my contract in November 2021 I was paying 699 per month new contract is 289 guess what I am now paying 733. When I inquire I am told I am still paying for previous phone which I was never told about this really feels like I was ****med @ MTN is this how you treat your customers? I cannot wait for the new contract to end I’ll take my loyalty somewhere else.