I was sold a PCP but signed for a fixed sum loan 😭

[Carlingcup]

Good afternoon, I would like some advice please. Last Friday I sent an email to Santander asking to voluntary terminate (VT) my contract which is financed by them. I paid £8795 deposit which was equity left from my previous PCP and now find myself in negative equity with 36 payments made from a 48 month deal, hence the need to terminate. I received and email back from Santander stating that I cannot VT as I have a fixed sum loan with PCP elements (balloon payment, mileage restrictions and a guaranteed value). I have subsequently complained as that is not what I signed up for but clearly I appreciate I have (a harsh lesson learnt). As mentioned, the dealership settled my previous PCP and they new I wanted the exact same deal with the same 3 options of a traditional PCP and more importantly, a VT option. Upon checking my paperwork which consists of e signatures by only me, of pre contact credit information, the loan agreement and something called a sales agency agreement which I recall is the only document that the dealer focussed on, mis-leading me into thinking I had a traditional PCP. I appreciate I should have checked everything before signing and I also believe Santander will throw this back at me. Although I understand that I will need to exhaust their complaints process before potentially asking the ombudsman to intervene, my question is, am I wasting my time pursuing this as I truly believed I had PCP with a VT option or am I banged to rights?