Migration from legacy Income ESA to UC, sudden letter from ESA Dual claim

Hello,
Please can someone help, as I'm getting no answers or help from ESA calls or from CAB UC helpline.
Was on full Income based ESA, with Disability premiums, since 2018.
Then told had to do UC Migration, submitted October '25.
Last week received ESA letter out of blue stating been put on Dual Claim, and now being put on Contribution based ESA, and part UC.
However, never been on Contribution based ESA since 2018, and ESA contact centre absolutely refused to explain why put on Dual claim with Contribution based ESA.
Told me they cannot say why, and refused to give ANY explanation or help.
Citizens advice are unable to answer this too.
Have spent several hours on phone to ESA and CAB, and still no answers.
I need to know why, having been on full Income based ESA for years, am suddenly told am getting Contribution based new style ESA, instead of getting full Income based UC as was expecting?
Also, Contribution based ESA only lasts 1 year, so what happens after 1 year?
Is there ANY disadvantage to being put on Dual claim, instead of full income based UC (eg, shorter Transitional protection, loss of free Prescriptions & Dental care, or other losses?)
Also, ESA had sent no letters about this, or how decision made, or how their calculations arrived at, or anything else. Only a decision notice stating now on New Style Contribution based ESA.
Can't get any answers from anyone at DWP, or CAB.
Please can someone help?
Thank you 🙏