UC migration - Income Based Support Group now changed to Contribution based?

Hi there - apologies if the answer to my query is on here somewhere I have been chasing my tail for a while now!

I have been in receipt of Income based ESA (Support group) and started the managed migration to UC last month. I am due to get a decision this week and first UC payment early next week. I have managed to budget for bills and food to cover the gap and had the last (2 week run-on) payment of ESA as expected.

Last Friday I noticed an additional payment of ESA had gone into my bank - different from my previous amount, I wasn't expecting it as had been notified that ESA and HB would stop due to UC claim.

Today a letter has arrived saying I am now in receipt of contribution based ESA (less that Income related) and have made numerous calls to chase this up without resolution. I couldn't get through to Help to Claim at all and have navigated the process so far just using the guide on this marvellous site.

I have not paid NI contributions from work for years and do not meet the criteria for CB ESA as far as I am aware.

How do I proceed? Is there any other way to contact ESA as they don't answer their helpline?

I have left messages on the UC journal.

Will this newly announced lower amount affect my transitional protection?

I requested to continue fortnightly payments, and have rent paid direct to the housing association.
They just replied (4 weeks after I asked) stating I have to ask the HA to apply for it via their portal; as yet no response from the Housing Officer about that and I don't know where I stand in terms of going into arrears while they organise themselves.

Sorry this isn't very concise but any suggestions and input at this point would be most gratefully received.

many thanks and best wishes to everyone facing this unsettling process.