Told housing benefit will cease - no reason given

I hope that this is not too off-topic, being about housing benefit.

I just got a letter this morning that has me in shock. It's from my local authority, and it told me how much council tax benefit I'd be getting, but under the heading of housing benefit, it just had zeroes, and it said, "From April 2nd you no longer qualify for housing benefit". I just don't understand it.

I'm on income based ESA, and PIP. I've been on income based ESA for years and was on DLA for years, then last year I began to get PIP. So basically, the only thing about my benefits that has changed is going from DLA to PIP. I've been getting full housing benefit from this local authority since 2010, and as far as I can see, nothing about my circumstances has changed.

The only possible change is that I reach 65 in late April.

I'd really be grateful if anyone can shed any light on this. I'd rush straight to the local authority's offices to ask them but it's Saturday, and I don't want to stew in worry until Monday. Thank you.