How to proceed after requesting a "rent increase" for a tenant on Housing Benefit

Rent Arrears

Hi,
This is a question for Simon, who's has more experience with social housing tenants.
We have a council tenant through "Direct Let Scheme", whose rent is paid by housing benefit directly into our bank account.
After almost four years, we requested a rent increase using Form 4 and sent the form to both the tenant and the council HB office.
Six weeks after sending the rent increase request, we still haven't heard of them.
From our point of view, the tenant is now in rent arrears.
Contacting Ealing council HB office for landlords is not possible by phone. They haven't responded to our rent increase request yet, although they acknowledged via automatic email reply the receipt of it.
What would be our next move?
If Simon or anybody else I n the team could help me, I would be grateful.
Thanks