Connect third party modem

[ggmiii74]

Whats the correct way to swap my rented mediacom modem to a third party modem? I've tried the self installed walled garden method and this does not work.  I keep getting the error  "Sorry, we are unable to access your account information. "  

[HighTech]

If the self registration portal isn't working for you, I would recommend to call or text Mediacom. 

Give them the new MAC address of your new modem.