Horrible experience with Virgin so far…

Engineer been out multiple times, changed the router last time he was here. WiFi still keeps cutting out regularly throughout the day. It’s madness. I don’t know what to do, he said it’s not normal but can’t find any faults! It’s cut out again now, light just flashing red! I’ve done all the factory resets, nothing seems to be making a difference. The only thing that I can think of is whether my other connected devices are causing it to drop out? I can’t believe how bad it is, and desperate for a solution! Help!