Do you have the expansion pack Heavensward installed and registered to your account, or were you on the 'early access'? When early access to Heavensward ended players who hadn't yet purchased or registered the full expansion suddenly found themselves with frozen levels and exp exactly like what has happened to you (as the expansion is required to level beyond the original level cap of 50).

If you do have the full expansion registered though, then this is clearly a bug and sadly there isn't much else that could be done I'm afraid - it would be entirely in SE's hands.