Received this call I let the answering machine pick did not leave a message.  Not sure who is callng

Got a call from this number and when I answered there was only silence. I held the line until the phone disconnected. I called back, after blocking my number, and got a recording saying "thank you for returning our call. However, we do not accept calls from blocked or restricted phone numbers...." Yeah, must be kinda annoying getting calls from people you don't know. I added them to my phone block.

received a call from this number,  caller id said only, upper marlbo, md.  they left no message.