Question about Google Pixel 3

Hello all I have the problem that I have no internet reception with my Pixel 3 64 GB via the mobile network. Everything works via wifi, but not via the network. The bars are full for me, but the 4g character is missing. I have already reset the connection settings in the settings. However, this did not help. I have also switched the flight mode on and off. Has anyone had the same experience and been able to solve the problem? At the beginning, everything worked perfectly. I have also installed almost no additional apps (except sbb, Netflix and Whatsapp)... Kind regards Emanuel