Internet disconnects and won't reconnect.

Hi I got a thing in the mail saying I need to take my modem in to upgrade it. It was a fat Motorola. I get a arris tm3402a. We also had to down grade to basic cable and got miniboxes. So install the modem and it would disconnect and we couldn't get a connection had tech come out and he tells us its the router because when he plugged it into my pc it randomly worked.

So a day later bout a 100 netgear wireless router. Already was seeing lesser soeeds than with my linksys. But then would dc and Id have to go upsta6 and reset modem. I would do this about 4 or 5 times  with resetting router as well. Then I would message via app and get told to reset modem another few times this time they would send a signal. It would work some times and Id end chat most tines it didnt and gave up.

I think it to be low connection via the cables to the mother cable wouldnt surprise me bc they are old. It could be the modem.

The tech didnt want to check the wall connections or anything he just wanted the easy answer. But soon as he left I having to reset. I am on my mobile data rn bc it still wont connect.