CH
Yes, allowance rates can, and do, change.
Yes, this one was notified in advance, originally through issue of a DIN.
This change is just one of a package of allowance restructuring introduced to coincide with the move towards common tri-service pay/allowances.
Yes, you have lost out, in order to free up money to improve DA and other allowances elsewhere.
No, you don't have a hope with a redress of complaint.
In the great scheme of things, occupying your own private accommodation is your own choice. Why should you expect to be paid a higher rate of DA than anyone else?
Sorry not to be more encouraging.
Regards
Ginseng