purchasing error

I have tried to purchase something with my refferal bonus money and then once i did this would show up everytime  

 “Request not completed”

“we noticed something unusual and for your security, this request could not be completed. please try again later, or visit our help center”

this message would appear Everytime i try purchasing something. I also waited about a week and tried again but the same message would appear Everytime, i tried factory resetting it but it still didn’t help and the same message would appear again.

My brother had thing problem right after i got it, but he just waited a few days and he was able to purchase again. So i did the same but for a week and the issue Still appeared.

pls help