Bristol Uni Gave Me an Unconditional Offer by Mistake

I received an unconditional offer from Bristol for Veterinary Science. Before accepting, I exchanged multiple emails and phone calls with their admissions team to confirm that I did not need to complete my Access to HE Diploma and I assumed this is because of my confirmed grades at A level. I even have written confirmation from them stating that my offer would not be affected as long as I completed the Access to Bristol Outreach Programme.
Based on this, I discontinued my Access course, accepted Bristol’s offer, and rejected my other offers. Now, they’re telling me I don’t meet the entry requirements because they realised I only have two full A Levels and an AS in Chemistry instead of three full A Levels. My UCAS application clearly listed my qualifications, so they had this information when they made the offer.
For reference I applied to Bristol University for Vet Science and received my unconditional offer 2 months into starting my Access to HE course in Veterinary Science and Zoology.
It seems like their mistake, but I’m now in a really difficult position. Has anyone dealt with something like this before? What would be the best way to challenge this?

Speak to UCAS as I believe if the offer has been made on UCAS they can’t rescind it and UCAS will support you on this

Yep, will definitely try to push back as much as I can. It is just a shame that with Bristol Uni this whole process has to be done through emails because their admissions office is a “faceless department” and don’t have a phone line either. Let’s hope their response provides some sort of solution.

Yep, will definitely try to push back as much as I can. It is just a shame that with Bristol Uni this whole process has to be done through emails because their admissions office is a “faceless department” and don’t have a phone line either. Let’s hope their response provides some sort of solution.