I've been having similar if not almost identical issues as well. This has been happening for me since WAY before COVID happened, at least since September or October of 2019.
Signed away my soul to a Cox Ultimate package and I'm consistently getting less than half the speeds I'm paying for. What I'm supposed to be getting is 300mbps download and 30mbps upload. What I'm getting is ~25mbps download and between 0-6mbps upload. On a good day, I'm getting ~130mbps download and ~20mbps upload.
The last technician who came to check out the problem around 2 months ago told me that my modem was working perfectly and my router was the one causing issues. I dropped $100 on a new router. Didn't fix a thing.
Every time I call Customer Support, I get the same basic questions, they reset my connection, as if I hadn't already done EVERYTHING that they are already asking/telling me to do, I get the runaround, and they tell me the issue lies with my hardware and it's not their problem, and they can't even send a technician out to check any cables outside. I understand them not being able to come into anyone's home because of COVID regulations, but they for some reason refuse to have people check on what's going on within my neighborhood outside of my home.
I've been paying in full for a fraction of the internet speeds I'm getting, and I'm sick of no one having answers for me.
I'm going to hop on a call tomorrow with billing and ask them to refund/reimburse me for my *** internet but I highly doubt they will give me a penny.