Verizon will not disconnected even if I have proof I paid for it
ummm have you try taking the receipt to the store and show them? try to get in touch with their supervisor maybe he can override. If it doesn't work, I suggest you unlock the phone and use it with a different carrier.
Can I unlock the phone even if the service is still active but suspended? ,
you can unlock and use it with a diiferent carrier. they only way you cant use it with a another carrier is if verizon block the phone and they normally do that when the bill is not paid in this case as long as your ex keep it on his contract, you will be fine.