Universal credit gone down

So I transferred from esa support group to universal credit last year and because I was on esa contributions based i also kept this.

I know because of transitional payment my award won't go up but this month it's actually gone down.

Previously I was getting £1574 with a deduction of £609 for esa leaving £965.

Now im getting £1574 and they are deducting £632 esa leaving £942.
I totally understand i don't get a rise on uc but I thought they couldn't take anything from my esa increase

Please help, thanks