galaxy s7 edge unlocked verizon phone adds a + in front of every incoming call?

[bloodydemons]

i recently bought a verizon unlocked samsung galaxy s7 edge phone off of ebay and bought a at&t sim card and using straight talk service but something is happening that has never happened before....everytime a incoming call it always adds a + and if i miss the call and click on recent call to try to call the number back it will not go thru insteads tells me something about a international call which it is not....can anyone help?