Housing benefit - no decision notice being issued

I have made a housing benefit application 18 months ago, & my circumstances have not changed. A decision notice was issued after a few months, and I asked for a reconsideration, providing additional information to prove their decision did not reflect the facts. This started a process of many additional requests for supplementary information over many months, each time I was asked this was provided promptly.

I became concerned they were never going to carry out the reconsideration as questions were being repeated, so I asked for the reconsideration to be completed and a decision notice to be issued.

Following this, I have only been told to await a response in due course several times. I have not been given a decision notice, and also no timeframe of when to expect a response, just to await one.

Whilst I appreciate the difficulties of the pandemic, I made the request for a decision 4 months ago and I don't even know when I should expect a decision.

How can I get the authority to provide a decision notice?
I am concerned that by not providing a decision notice, my claim has been put on hold indefinitely, & I cannot act. Whether this is to accept, appeal, tribunal etc.

Any help on what I can do, or information as to what they are obliged to do and when, would be much appreciated.