Internet speeds dropping for no reason, nothing has changed in our set up. Unacceptable for what we pay.

Posting again one month later with no resolution or improvement. We pay for the 1.2 GB internet plan. We run it through a Google Nest home wifi system with multiple extenders. It has worked great up until the last month (been running it like this for over 3 years). We routinely would get speeds over 600 Mbps and usually over 800 when testing closest to the router on devices running on wifi. Speeds usually in the 200+ for devices far away from router (3 floor house). Over the last month or so speeds closest to router are now not reaching even 100 Mbps and often not even 50. Nothing has changed in our set up and we have tried unplugging/resetting the Xfinity router and Google router multiple times. Would like to know why speeds have dropped so much especially given what we pay each month and how to fix it.