GalaxyA71 suddenly wont connect to internet

I was a sprint user but changed my sims to magenta tmobile  a while ago. My phone has been unlocked for few months and suddenly 50 percent or more of the time won’t connect to internet to email to make calls only emergency. I have tried the trouble shooting tips. Has any one else had this problem. I am not good with any technical stuff. Do I need to just get a new sims card? Help I need my phone for gps for work on monday.