You may find these to be interesting reads:
https://arstechnica.com/tech-policy/2021/02/cox-cuts-some-users-uploads-from-30mbps-to-10mbps-heres-how-to-avoid-it/
Many people report a similar experience to yours, including me. From what I’ve read and learned myself, the solution is varied. For example, I had to change my connection from coax to fiber in terms of the incoming line feed to my property. It took 7 weeks which involved running lines underground and in the air from across the street. For others, it could be related to things mentioned in the articles above.
Good luck. Happy to chat directly if you want more insight into my resolution.
