What is the point in contacting? Valve already told them what situation is.
Valve is company that have right to do what is it sees right, nothing illegal in that. His ban will still hold forever, he better just accept facts.
Jamppi isn't first guy telling them "It was friend who cheat / I sold account to friend who cheated", endless list of them.
Valve knows that if they start give people second chances (even if they say "wasn't me, I sold my account), their qualifieiers and tournaments start to be full of cheaters like matchmaking is