I ve bought duels entry and player named anqiuMTofERA#3400 hitted me with weapon with 100 damage in face 1st turn. Posted ticket, support rejected refund, told me to submit as bug. Did not take SS cause I left shocked.
This is a known exploit, posted by Blizzard here: 28.4 Known Issues
It is why they have disabled the Heroic Duels. You should have been able to get a refund.