Just tested it myself and everything seems fine. You only gain a charge when the opponent is not stunned, so if you're parrying and then immediately throwing a heavy, then you probably won't get a charge. Gotta delay a little bit.
wait didn’t he gain a charge in heavy and 2 charges while’s opponent is not stunned
No
I believe it’s one charge per heavy hit on a non-stunned opponent - so if you parry-heavy you can get a charge off the second hit, if the stun wears off after the first hit locks them into the animation.