I got a call from this # - I called back and they said they were the "UMA" corporation and gave me another call back # of 877-643-6608.  A quick google search reveals that this is a company called United Management Associates and they are a debt collector.  Apparently they're trying to collect a debt from someone that lived in my home and/or had my # before.

Unless they provide you with writtten proof of debt per the FDCPA they are more than likely a fraudulent scam.

This user is blackmailing me with some nudes of me

What user?  The person that is texting you?

Person is telling me they sent an overpayment for their check and they need me to send them the over payment amount to them.  If I sent them the money I would find out later that it was a bad check. So, they'd be scamming me out of money. (That's what craigslist scammers do).