NCO Collections Agency - NCO Financial Pressuring me to return cash I didn't spend. Nationwide

Let me outline the variables of my situation. A will be paypal account #1, B will be paypal account #2. I've used paypal account A longer than B, B is the account I have a negative balance on. I have no bank accounts or anything of that sort attached to these paypal accounts.

I trade various internet items through my paypal, buy and sell, nothing over $100. Infact, the highest amount was $71. So I have a bunch of ancient transactions in account B and suddenly it ends up in a negative balance. I do not know how, I've not used that account pre-june yet there is transaction history from june. So apparently there has been a chargeback of sorts from a ghost email, a ghost person tannuyen@gmail.com.

Now here is where I get screwed, NCO starts calling my cellphone, every morning. EVERY, MORNING. I finally accepted the call on my cell (god knows how they got it) and we talked, I said I was not going to pay this because I didn't use this account forever and blah blah, she then says "okay we'll keep calling you."

They sent a letter to my old address, I've not lived there in many years.

I want to stop these people, I don't want their calls, I don't want them wrecking my credit, I don't want them to send me letters and I refuse to pay this negative outstanding balance of $71 on a paypal account that's existence has barely been acknowledged till recently.

HOW?

Marcel
Brampton, Ontario
Canada