Problem with answering machine on Panasonic Model # KX-FPG376

I purchased this model in 2004 when I opened my business and never had a problem until now. I went on vacation and now that I'm back the answering machine doesn't seem to be working on the unit. Here is specifically what happens:

When receiving some phone calls, after 2 rings a random answering machine message starts playing through the headset-- even if I have answered the call. It is a generic "hello, we are not available right now. please leave your name & number after the beep." It sounds like the kind of message that is usually standard on an answering machine before someone records their own message. My own recorded message is still on the unit, but it never picks up.

I have tried everything I know to fix this. I have my users manual. I reset all advanced settings to the default, I unplugged my unit, and made sure that it was set to TAM/FAX. It is currently set to pick up after 4 rings, but with this random computer voicemail picking up after only 2 rings, my calls never make it to the unit's answering machine. People can obviously leave message on this ghost answering machine, but I have no idea how to check them. I intentionally left a message on the ghost answering machine but when I hit "play messages" on my base unit it said there were no messages to check.

My phone line doesn't seem to be the problem-- I can still make outgoing calls and my caller id and call waiting are working. I receive incoming calls-- but after the second ring the ghost answering machine always picks up.

Any ideas on what the problem/solution might be??

THANKS!