Cheating company

We have a contract with MTN and have been since over a year. All this time we were able to get 5G on the contract and since 26 April, our service is now limited to 3G. Now I am being told there is no 5G coverage for our area, what utter nonsense if he had it for over a year????? MTN is cheating us as now we have to apply for a more expensive contract.