CA as income for UC after CA payments stopped & other income

Client used to receive CA until 2020 (with last 2 years being overpaid CA).  Claimed UC from Dec 21, had CA and some mysterious £215 income taken into account so got no UC whatsover for herself and HCE was short too until she got LCWRA. She told UC from the start that she was not getting CA but as usual it was left to client to contact CA.  She then got a letter dated April 2022 saying that her CA had stopped in 2020. UC was adjusted as if she only received CA up to date of this letter. Called CA with client, they said that they will send message for a proper ‘hand-off’ to be done which would provide UC with actual end date of CA, but that there was no time scale for doing this, even though the request was marked urgent.
If nothing happens soon, who should we complain to, CA or UC or both? 
I have raised a CA Evidence Form about this lack of communication between CA & UC but don’t know if they are interested in that

Hi Andrea

Just my two cents but I think UC are at fault - onus is surely on them to accurately check what the CA system says when calculating payment. I had a similar scenario where CA was suspended (not in payment) for some months and UC took it as income because they didn’t properly check the system. Called CA and the worker confirmed that it happened a lot and the fault was with the UC end and that they do have access to the relevant info.