iphone 11 pro max imessage problem

my imessage wont work anymore i just bought my phone and my imessage worked for the first 3/5 days and now when you go into messages, and you try turning imessage back on it keeps saying imessage unsuccessful. brought it back to the t mobile store to see if they could help and they did some basic check over everything and tried to help and my facetime wont work either.

can someone help??? everything is updated. and i tried restarting everything too not sure what else to do.