Hello. I'm sorry that you had such a sad experience using Teltonika devices.
According to your situation, I recommend you to set up a router with antennas and a power supply from the kit. WiFi is pre-configured on all devices, the network name and password are usually printed on the label of the router. On the latest firmware RUTX_R_00.07.00 and RUTX_R_00.07.01, after installing the SIM card, Internet access immediately appears. Accordingly, you can get Internet via wifi via LTE connection without any settings at all.
Can you write step by step what you are setting up and what exactly is not working?