person calls and tells me i have until 9pm to call back or else, they do not leave a company name, or the purpose of the call

We just moved to a new house, and we are getting repeated phone calls from this number asking for someone who doesn't live here.  They said they are debt collectors from Harvard Services.  I've repeatedly asked for them to take me off their list, yet they keep calling.

I got at call from this #, someone named Nate left a voice mail saying that I needed to call back right away and left an ext of 2077 and a referance #. I called back and they said they were with Harvard Collection Service and had my SS # asking me to confirm. I did not confirm nor reveal any information. They spoke very fast and agressively trying to tell me we had to resolve my credit issues today. I repeatidly refused to provide any further information, they were mad and we hung up.

From other things I've read on the net about this company I think it was a scam to get more personal info.

called said they have called many times but do not leave company name and say that i must call by 9 pm or else