Called an hour ago and left no message.

called on cell?  no one responded.  i hung up.

Called on cell. No one answered at first. After approx 6 seconds a recording played pitching a reduction in credit card interest rates.

I hung up.

This is an "interest-reduction" / "debt-reduction" place.  Some of these are borderline scams.  Some are legit but pointless since anyone could do this on their own by simply calling their creditors under hardship.  I wouldn't worry on this one other than the nuisance.  Just opt out or block their number.

This is a software generated VOIP call that can not be traced to the crook who is attempting to find someone stupid enough to fall for the bait of a "new low interest rate credit card."  A computer determines if you answer the phone, and then the call is directed to a con-artist who starts with the lies and scam. (This is why you will not immediately here someone when you say "Hello..." It takes a moment for the computer "robo-dialer" to forward the call to an actual human being, the crook.

They do not have to comply with the "Do Not Call Registry" because they are thieves.

If the unsuspecting idiot answers the call and says "Yes, I would like a new credit card..." that's when the crook starts asking for personal information in order to engage in the act of IDENTITY THEFT. And minutes after the person provides their personal information, typically the physical address, a work address, an account number, driver's license number, full name, date of birth... THEY GET ROBBED.

Lesson here is DO NOT ANSWER ANY CALL FROM AN AREA CODE YOU DO NOT RECOGNIZE. IT'S ONLY A CROOK CALLING.