If straight talk is gsm nexus should be fine. Sucks they tried to screw ya over like that. They have been surprisingly decent customer service wise to me at least. I lost my phone a couple months ago but they worked with me at least allowing me to redo my contract to get another discounted iPhone at least.
Most cell companies will screw people over though, no way around that. My bro has AT&T at full price and I think it's crazy. Whatever