Hi Mab
I'm sorry you find yourself in this position. Unfortunately, there is no legal timescale for the DWP to respond to a Mandatory Reconsideration, so they can take as long as they like. And yes, it is very unfair.
The only thing I can suggest is that you contact your MP and see if they can contact the DWP on your behalf. Sometimes MPs have success in hurrying cases along.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems