If both routers are going to do actual routing, you've got problems from the start. There are three solutions, either of which should work.
1. Use only the Mediacom wireless router. If it can cover the area you need, there isn't a reason to have another router in the mix. If it won't cover the whole area, you could configure the Netgear to extend the network.
2. Call Mediacom tech support and have their router configuration changed so that it becomes nothing more than a cable modem and use the Netgear for routing. Downside is if you are signed up for their phone service. I think, but don't know for sure, that the phone service requires using their router for all functions.
3. If you don't have their phone service, just get your own cable modem and use your Netgear router. If you do this you'll need to call Mediacom to provision your new cable modem. Make sure you get one that is compatible.
Note that if you choose options 2 or 3 Mediacom tech support won't be of much help if you have a problem with your network in the home.