Help c7800 router

Having a problem with my c7800 the main problem is that now my internet will just shut off randomly. I've never had this problem and I think it's my isp but I just wanted to make sure I didn't get a defective product. I paid over 500 for it so I just wanted to make sure. Recently my isp Comcast had a huge outage in my area and I think they are still recovering from that but they (Comcast) tells me it's not their fault and they keep wanting to send out techs which cost 70 bucks and usually they don't do anything.