Getting error code 97

I have been with straightalk for 12 years,have gotten new phones several times.I keep the same number,i have had this phone a little over a year.I live at the same place.As of 2 months ago my texts frequently won't send the error code is 97.When i try to make a phone call i get an automated voice that says Sprint will now connect you to complete your call with a pin number or credit card.I have minutes on my LG Treasure,straightalk with Verizon as the carrier..This is most of the time and people tell me they have been calling me for days,yet i show no missed calls.There is always a triangle in the top of phone then it indicates my phone is roaming.i have disabled roaming per instructions on the numerous times i have called customer serve.Customer service wants me to call them when this is occuring.I cant make them understand when this is occurring the phone will only allow calls to Sprint.So i called them and thier answer is that i am not a Sprint customer and they cant help.I have tried everything customer service has asked me to.Can you help or is it time for me to change phone carriers