Well, i guess you had your data exported before deactivation. Why not send a separate email for every post you made, asking them to delete the 'specific data', namely the post?
I think everybody should do that after deletion. See if they react a little more forthcoming when the inbox gets flooded. And why do they think that article 17 doesn't apply to them? The only loophole i see is that they call on article 17 p.3d, for archieving purposes. But that would be a stretch before court.