It doesn’t let me connect online with my friends on my tablet

Hi I want to report an issue that I hope you guys can fix it soon has possible me and my friend happend to the two of us as well. We sign up on Xbox online but on are tablet. And so everything was going normal we could connect. We put a username that we wanted and all of a nothing it changed are usernames and now it doesn’t want to let me enter to my friends file she erased her Minecraft game and she had awesome builds just so she can joined with her other friends and I don’t want to do that if you can help me connect with my friends and get my username that I had before without erasing my files.THANK YOU.