Netgear AC1750 Wifi Cable Modem Router C6300 problems connecting

Hello,

We recently installed the Cox Ultimate plan. We looked on the list of Cox approved modems and found the AC1750 combo, which also says on the box that it is approved with Cox. When the technician came out for the install he was unable to get it to connect. After about 20 minutes of trying, he said it must be defective and gave us a modem to rent. I've read that some people were having the same issue but have yet to see a resolution. Was it truly a defective modem or is it an issue on the Cox side that can be resolved? I'd like to know before I return it to Best Buy and buy a different modem. Thank you very much for any help you all can give.