Who called from 2012839713

Called my cell..didnt leave message..I dont answer unknown numbers on my job

Call came to my cell phone.  Cell numbers are not listed, so how are unknown people calling my cell.  There are very few people and businesses that have the number.   I do not know anyone in New Jersey.  My phone rings 4 times then it goes to voicemail if I don't answer.  I didn't answer, but there was no voicemail from who ever this is.  I also get calls from unknown numbers in Puerto Rico,  I do not know anyone in Puerto Rico.

should i call back the number? i feel like it has called me once a few weeks ago. its super creepy and they arent leaving a voicemail..

Called my Plano TX Skype number and it rang on my iPad in Malaysia. No message. Nobody I know!

Missed the call, but no voicemail. Seems suspicious.