No it is not. That would be a violation of the
Fair Debt Collection Practices Act.
They CAN, though, call a neighbor to ask questions about you.
Report violations of the FDCPA to the FTC and your State Attorney General.
...but before you do, talk to a manager at the collection agency and tell them of the violation and offer to be mum about it if they'll pay the bill for you. I've seen it work!