WA seems to work ok, means you can send a WA mesage when Wifi is not connected?
Such a sudden interruption to me sounds a bit more like a reception issue, unless it occurred directly after a system update (version you have installed if very new…).
However, have you tried the other SIM slot? Have you checked your APN have not changed, i.e. check if entered as indicated on the network providers HP. Maybe try to reset the APN to default (three dots in the APN settings), just make a screenshots of the current entries. Can you test another SIM card (better different provider)? before this update there was a bug for some user which could be solved by adding a second SIM and then it was possible to change the mobile preference from always ask to the preffered SIM…