Return new modem

I saw an offer to upgrade my modem on my xfinity account at no extra cost, so I ordered it. I absolutely can't install it and must return it. The new modem isn't listed under devices I can return in my account. I must return this modem asap so I won't be charged. I can't drive to UPS so it must be a "from home" return. I recently had surgery and can't drive yet. Please help me return this new xfinity mode from my home so I won't be charged. It has been a month since it was sent to me. My neighbor incorrectly got the package delivered to her house and forgot to give it to me until this last weekend. I can't afford to be charged for it. Please help me return it! Can I just put it in the original box and send it back somehow?