If you have gone through all the solutions and still the error persists, you should get in touch with or call your mobile carrier. You should explain your problem to them, and they will be able to help you investigate the problem and solve it. It depends on the complexity of the issue, this can go from a couple of minutes, or it can drag on to a couple of days. Either way, contacting your mobile carrier is the best way to solve the problem.
Moreover, it might be possible that you have to replace your sim card itself if the error continues to happen/priests. It would be a safe solution to replace your sim card with your network provider as soon as you got the issue.