Very bad service and communication

We app**** for "private to private" vehicle finance, and received and email confirming we were approved on 9 July 2025. The seller had to submit certain documents which was done. We now wanted to finalize the deal, including certain additional VAP's ect. We attempted to contact the sender - SS - Insurance and finance marketer - with no luck. We then started calling various numbers and email different people but to no avail. We need to clarify some details, and upgrade the warranty. It is just impossible to get hold of anyone, and if by change a customer agent do answer the telephone, he or she is not able to assist, but would rather make promises to get the correct person to contact us. Up to now this has not happened. We do not know what to do, except to escalate this in the hope of getting this deal either finalized or cancelled.