It sounds like H & M probably compared notes about you and have both decided on non-contact is best.

I suspect your interpretation of the situation and theirs probably differs quite alot.

It sounds like it could easily have felt like a manipulative environment. comparing one against the other.

I am not sure there is anything you can do. They clearly don't want confrontation.You say H is calm thoughtful and considered so it's unlikely they just came to this decision on a whim.
You could perhaps appeal for closure, an explanation with a promise not to continue to chase the situation if they agreed.

I can see your obviously quite stunned and hurt about it, but somewhere along the line you seem to have missed something. Perhaps a conversation you had in the weeks leading up to them blocking you.?

It's tough to make a call with only one side of the story, hope you are able to get your closure and move on.