Comcast Compatibility - Configuration Questions

I have gone through a little over a month of trying to get my new Netgear modem/router to work with Comcast and I have not been successful in getting it to work reliably.   Sometimes it works, but in the latest round of problems, the cable modem/router went offline from Comcast in the middle of the night and lost the connection to Comcast.  Netgear support told me that the Upstream Power Settings were too high and I needed to tell Comcast to reprovision the modem/router.  I was on the phone with Comcast for over two hours and they tried several times to reprovision it but were not successful.  I'm caught in the middle between Netgear and Comcast.  Netgear says it is a Comcast problem and Comcast has been unable to do anything to resolve it.  I have decided that it is two difficult to get the Netgear modem/router to work with Comcast and I am going to return the Netgear modem/router for a refund and go back to the equivalent Comcast modem/router. 

How do I go about returning the modem/router to Netgear for a refund?  It is a little over a month old.  I purchased it at Best Buy; and unfortunately, it is outside of the Best Buy return window.  Please let me know how I can go about returning this to Netgear for a refund.

Thanks,