Please I cant make call out with bonus since morning,why please?

I have momo recharge bonus but I can't use it. I am told that my account balance is not sufficient to make calls

I can't make calls with my MTN sim this morning, I even tried to reach the customer care center but it's just hanging

Have been using my sim to cal and it all when well but this morning I tried using it to can and it said have been banned from making calls