Who called from 3154441002

Called my cell just now.  Did not leave a message.  Called number back and got fast busy signal.

Student loan consilidation people.  I've already told them I'm not interested but they keep calling.  They don't leave messages.

They have called me like 10-15 times.  No one says anything. When you call back, it just says "all circuits are busy".

They called saying they are a loan consolidation...they knew my social...should I be worried???

This number is calling my cell phone very regularly.  If I answer, they hang up, if I let it go to voicemail, they do not leave a message.  If I call back, a recording says "all circuits" are busy.  What is the point of this?  If it's a scam, then what is the angle?  Any info would be greatly appreciated.