ESA "change in money coming in" letter

I would be grateful for anyone's input on a letter I had this morning from the ESA people - I don't understand it at all, except that it indicates I'll be at least £1o a week worse off, for no reason that I can see. The letter is as follows (brackets mine):

CHANGES IN THE EMPLOYMENT AND SUPPORT ALLOWANCE RATES PAYABLE

We have looked at your claim again following a recent change (there has been no change)

From 14 Feb 2018 (2018?! It's 2020!) your ESA will be £180.50 a week
This is because of: a change in money coming in.

From 11 April 2018 your ESA will be £182.85 a week.
From 10 April 2019 your ESA will be £184.80 a week.
From 8 April 2020 your ESA will be £187.95 a week.
From 15 April 2020 your ESA will be £170.85 a week.

This is because of: a change of money coming in.

We have used the tax years ending 5 April 2010 and 5 April 2011 to assess your claim (what?!)

We will credit you with National Insurance contributions while claiming ESA.

The payment of ESA is based on your National Insurance Contribution records and any additional amount the law says you need to live on.

You have not paid, or been credited with, enough National Insurance Contributions for them to be used in this assessment.
___________________________________________________________________________

So. Any insights? I honestly have no idea what they're going on about.