The exact words OP is looking for are "This disrepair is affecting my right to quiet enjoyment of the property". Send it via email, then you have a written confirmed dated record of serious disrepair, assuming they don't jump on it Monday.

If the HA doesn't take it seriously, the council likely will. There are also many 'no win, no fee' outfits who will take a slam dunk case like this if it's left unfixed.