My speed dropped to less than dial up

I have the 2000Mbps plan. I got a new modem up that supports up to 4GB. After activating it, my speed dropped from 2GB plus for the last 8 weeks to 37.5Mbps. I have restarted modem multiple times. Best speed I have been able to get when connected directly to modem via Ethernet is 983, and that was only for a few minutes. The soonest appointment I could get was a week out. WHAT IS GOING ON