Why should a GM join mumble, the presence of you too there wouldnt explain the situation you are into.
Besides, i wouldnt join a teamspeak, mumble or whatever just cause someone told me to do so.
If you have followed the instructions, everything would have been just fine, so why blame the GM, you were the person
who acted wrong.
Calm down, ask nicely, there is always a way of solving those issues!
all the best, Kim