Netgear router reboots multiple times a day

The Comcast Business provided routers are recycled devices that include port forward setups that cannot be removed.  The problem has cost $100's of dollars to attempt to correct.  He finally convincedcomcast that the used machine still had addresses from a prior security client,  Comcast sent out a rep who agreed that hate device had not been serviced after removal from a  prior Comcast client office.  He still could not remove the old port forward settings that someone else had set.  Comcast said "to bad" rchase a new unit if you do not like what we supplied. I still cannot find which routers are approved for use with Comcast business.