1) Please try to send an SMS from different device using that sim card first.
2) Check whether SMS storage is full. If it is, both receiving and sending SMS stops working. You can check it in Services → SMS Utilities → SMS Management → Storage. Clear up some space if it's full.
3) After that, check if your SMS limit is reached. If so, SMS limit can be cleared in the Network -> Mobile -> SMS Limit WebUI page.
4) Also it's worth contacting your service provider to check if everything is working on their side.