Loan and collection agent

I was owing the bank about $50k credit card for 7 years. Yesterday ,
collection agent called me for repayment.

My question is that. 1. How can they found me. ie, got my contact no and
address. I was hiding for 7 years.
2.I paid in full with bank A. but I am still owing anther bank B money.
I am afraid that the bank B know that I settled the loan with Bank A. Will the bank A share the information with Bank B? (I meant the collection agent)
3. The bank A knew my new address now. Will they update my information
to Credit Reference Agent?

Now i got no money after i settled the loan with bank A. If bank B chase up
the money. What can i do??
Pls help