ESA Underpayments Advice?

Hi Everyone,
I wonder whether someone could help me please? I've received a letter & 45 page form from the DWP about my contribution-based ESA being eligible to be checked to see whether I should have received Income-based ESA from my transfer from Incapacity Benefit in February, 2014. They say they sent it on 27th November, but I only received it on 15th December, & have been much too ill to deal with it until now. The deadline is 17th January & I've just begun wadding my way through the form. It's incredibly detailed, with masses of questions that require me to remember details from the past 4 years! Some of the questions I just don't understand. I understand they need this information, but they really do seem to be making ill people jump through hoops & make it as difficult as possible to apply for what was probably owed to us in the first place. There is a helpline, but I just don't trust them to help me fill this form in to my best advantage. Is there a Benefits & Works guide to help members fill in this gargantuan form? I don't know who else to ask.

Thank you Gordon. I'm wadding my way through it and making notes of the questions I don't understand. I'll post them here when I've sorted through them. I have to keep stopping filling in the form as the arthritis in my hands means I can't hold a pen for long. Also, brain fatigue knocking me for six today!