There is a formal appeal process if you want to challenge a decision about universal credit

The minimum income floor applies to some universal credit claims if you are self-employed. It does not apply in all cases. If the minimum income floor applies, you may be treated as earning a certain amount even if your actual earnings from self-employment are lower.

For universal credit, if you are an owner or director of a limited company you may be treated as though you are self-employed and the company income treated as your self-employed income. 

The benefit cap is a limit on the total amount of working age benefits that you can receive. If your universal credit is over the amount of your benefit cap, it might be reduced.

Universal credit awards are made up of a number of different elements. The elements that are included in your award depend on your circumstances (and your partner’s circumstances if it is a joint claim).

This part of the website explains how universal credit works if you are self-employed.