Unknown numbers on outgoing calls list

I just recently found that there are some outgoing calls on my call log from several different 800/877 numbers. I tried Verizon but they couldn't tell me why it was happening or how to stop it.  I tried reverse # look-up but I don't want to pay to find out it's just a spam #.  {edited for privacy} is the worst and they seem to be running some kind of wells fargo scam from the complaints about that #. Still doesn't explain how they can use my phone line for their calls. I tried calling that # but all you get is a loud noise.  Anybody know how  to stop this hijacking and prevent it in the future?