If you need Verizon signal for a Verizon-branded Note 4, your best bet is to take it into a Verizon store and have them look at it. They should be able to get it fixed up and running without any problems. I bet even if it is out of warranty they could do something for you if you are looking to buy service from them.
Since you've had it for over a year, it's obviously out of warranty, but it should be pretty easily fixed as long as the hardware wasn't defective when you bought it.