I to have an RCA tablet that I had to do a factory reset on earlier this year. I kept putting in the gmail address and it didn't recognize. Today I tried again after several months. I put in my cell number and got a screen that said "Google couldn't verify this account belongs to you. To recover your account go to:
https
/g.co/recover for help. I went to another computer and followed the instructions. I made sure my gmail address worked on the other computer. Went in and updated my information again. Then I went back to my tablet and it let me sign in and recover my previous apps. Hope this helps.