I have minutes left,but i can’t make any calls

Hi,I’ve tried to call,but there’s always this message saying that I’ve reached my capped limit,so I must pay or increase my extra usage limit. The problem is,I’ve got a lot of minutes left,I’ve never been late with any payment (even the latest,it says I don’t have to pay any extra) and I increased my extra usage limit (just to try solving the problem). I don’t understand why and how is possible.