ESA to UC migration statement / payment question

I have recently had to migrate from ESA to UC and I think I have an issue with my first UC statement / payment but I just wanted to check with someone on here before I do anything as I may well have misunderstood what I should be receiving.

I have been in receipt of ESA and in the support group for over 10 years. My usual payment since April uprating was £323.50 per fortnight but since migrating I have received £281.10 per fortnight so am now worse off.

Prior to starting my migration I did an online check to see what I was likely to receive on UC which suggested it would be;

Standard Allowance - £400.14
Disability Or Health Condition - £423.27
with £609.05 then taken off for ESA.

However my first UC statement reads;

Standard Allowance - £400.14
Transitional Protection - £0
(Your Universal Credit entitlement is not less than your previous benefits, so we have not added an extra payment)
with £609.05 then taken off for ESA.
I have therefore received no payment for UC this month.

For context I have a single claim with no dependents, no housing costs and no other income. There are no notes, messages or outstanding to do’s on my journal.

Please could you advise if you think that an error has been made on their part or my part.

Many thanks.