LM1200 WAN connection drops after 10 sec regardless of what I connect it to

I bought a LM1200 three days ago to use a LTE-backup when my cable modem fails.

I have for three days now tried to get the damned thing up and running and I´m seconds away from smashing it ans sending the pieces in a package to Netgear as a thankyou for nothing.

Everything works except the WAN-port does not accept any type of connection. Actually it connects to whatever I connect it to and it gets an IP-address but after 5-120 seconds of showing a green light both in the admin app and on the LM1200 it simply just drops the connection.

Right now I´m about to smash the crap thing just to get the satisfaction of smashing it to pieces. It has the latest firmware. And a message to Netgear...next time I will not buy something with your logo on it!!!