Unlocking iPhone 6plus

[cty109]

I have a Verizon iphone6 plus that i purchsed through verizon a while ago. I switched it to straight talk. After a while i got off straight talk and want to go back to Verizon but straight talk has a lock on it and won't release it. Is there a way to unlock my phone?

 

[rgd1101]

Only straight talk can unlock it. Why won't they release it?