Modem connects to phantom IP address

I'm on day TWENTY...working with my IP provider to figure out this oddity.
I wanted to upgrade my dsl speed with my provider, so they contacted our phone company to make the switch. Instead of an upgrade, I lost connection completely. So in the midst of my trouble shooting, I reset the modem to the factory defaults, unplugged my router and...my internet connection was restored...to the wrong service provider...no one seems to know WHO I'm connecting thru. My assigned IP address is a
192.-.-.- address...the one I'm connecting to is a 50.-.-.-. I'm assuming it's an unassigned address from the phone company. I've gone back in and manually input my service providers info in to the dsl modem and it automatically disconnects me from the internet....clear it out and I'm up an running even though my provider doesn't see me connected to their server. Right now...I'm getting free internet and I wouldn't say a word EXCEPT I'm still connecting at the original speed. The phone company "claims" to have fixed the problem on their end, yet my modem STILL connects to this 50.-.-.- IP address which is not my providers. I SHOULDN'T be able to connect...I'm not inputting ANY user info or passwords. Any suggestions for the "tech's"? They're telling me that my connection is impossible, yet I'm still surfing daily.

The modem should never connect to a 192.x.x.x address. That's an internal address your PC should get, not the modem. The modem WAN port should get anything other than 192 or a 10.x.x.x

The ISP should be able to find out who owns the block of IPs you are getting and figure things out from there. Phone company and ISP need to sort this out.