Gigabit slow speeds

I’ve had this problem going on 2 months now and had several techs come out to my home to check what the problem is and none of them could diagnose the problem. I’ve had several modems replaced to see if that resolved the issue and it hasn’t. I had a senior tech here the other day and he wrote up a ticket for a line tech to repair the line but Im not sure if he did anything as I wasn’t home when he rang my doorbell on my nest camera. A day later I get a call from him saying services were repaired but speeds were worse. I’ve ran several speed tests and only getting about 400mbps download speed. My upload speed is where it should be. Idk what else to do but it’s frustrating paying for a plan I’m not even getting the product I’m paying for. What can I do to get this resolved/fixed?