I've had my account stolen and I want to know how I can regain access

Recently, my brother was playing minecraft, when he had his account hacked. upon further inspection, the hacker has deleted his microsoft account (registered under gmail) and since then we have had no access to his account, or minecraft (since his account has been deleted). We have proof of purchase (for minecraft), and we would just like to know if we can regain access to our copy of the game. Thanks!

:)