LB112o modem and AC1750 router connectivity.

I bought a LB1120 modem and put a T-Mobile sim in it. I have exellent T-Mobile coverage in my area. I got the data set up with no trouble and getting 4-5 bars. my problem begins here. I connected the modem to my PC and it says I have internet but when I look up anything it loads for a long time and then says connection was reset. I've checked proxies and other solutions for this error but nothing has worked. I then tried connecting the modem to my AC1750 router and when setting the router up i either get a internet not detected problem or it goes through fine. when the router goes through though any device connected to it doesn't recieve an internet connection but the router itself says it has an internet connection. I have opened a case (#43397266) but no reply yet. this is getting frustrating. Any help is greatly appreciated.