Normal. Your phone line now is compressed, or uses voip to carry the call over the cable service.
Most modems are not compatible with VOIP.
Or better, most VOIP providers do not support data (modem) calls over their network.
That phone line (warner cable) is intended for people that already have internet via cable service (one of the best services around, until it breaks and takes a week to get a technician).
The good news: If you order more than one service, they give you a break. Internet and cable TV goes for about the same price than cable alone..