new modem/router activation

I'm trying to activate a new modem/router and the customer service rep kept getting an error.  She said she wasn't able to remove the existing modem from the account. I don't know if it's an issue with the new modem or on the service/account end.  She attempted to transfer me but the call was disconnected.  Is there a contact number for someone involved with more technical experience?  I'd prefer not to go through the same process with a new rep just to get transferred again.