If you're seeing 90+Mbps max hardwired, it's usually an indication that your network card is either set to 100Mbps max or it needs to be upgraded. If you were able to see 250Mbps on your machine with a rental modem, then I'd suspect a configuration error on Comcast's end. What modem are you using now?
I've asked a Comcast employee to review your account and check your modem status. You should expect a reply in this thread.
If you feel like doing some troubleshooting on your own: See the troubleshooting guide.
Hello Jellotot. I can assist in troubleshooting your speed issues with your / these modem(s). To get started, please send me a private message and include your full name and account primary phone number so I can access your equipment.