terrible internet speeds

Hi, I pay for the 250 Mbps plan and can't achieve speeds over 20 Mbps download and usually even worse than that upload. It's a roll of the dice if I'll even be able to get 2 Mbps some days. I've done speed tests over wifi and ethernet on a variety of devices that with my previous apartments wifi were able to get Gbps speeds, so I know it's not an issue with my devices. The online support was not helpful, just had me restart my devices and router multiple times even though I had already done that multiple times, but then told me a technician coming out would cost me $75 if they didn't think it was an issue with their equipment. Which I am not going to pay for on top of my $120 a month wifi I'm not even getting, has anyone dealt with this before? And did you end up having to pay for the technician? I just moved in and it's a cox supplied router so it's not personal equipment, but I don't know if they'd blame me for bad wiring.