888-407-5724

no caller ID since they call my cell phone.

They leave a message.  Their software is too stupid to wait for the beep, so the beginning is cut off.  I looked elsewhere for this message, and I found the complete message.  I will reconstruct the message's start.  I hear, "You have paid for your computer technical support few months ago.  We are <END RECONSTRUCTION> calling to refund your money as the company has been ordered to close down.  Please, call our toll free number 888 407 5724 to get your refund.  I repeat 888 407 5724."

I do not call them back.

Note the complete lack of a company name; this is a big red flag.  Based on their action on other numbers, they will try to get you to let them access your computer.  This will be either for identity theft (personal info), general theft (steal bank account numbers stored on your machine), or to install malware (that they will later charge you to remove).  Do not grant  them access to your machine.  Do not call them back as this is a SCAM.