i forgot my old PBE account user name and now i have no idea how to get it

last year I think I made a PBE account and now I wanted to log in and I forgot my username and I searched my email which I got from riot saying "you are now a tester and can play on PBE..." I forgot all this because I try to update the pbe account and it was updating with the speed of 50kb/sec . and after that, i just gave up on it. but since there is ARUF on pbe I wanted to play it but I forgot all abt the account. :/