How can I help with this please?
There are dangers in failing to pay the finance. Whether Vauxhall is in breach or not has no impact upon your liability to pay. They are just the loan company and the fact that Vauxhall are in breach has no impact on them.
The warranty might well exclude this particular type of fault. If it does then it can’t be relied upon.
You would still have statutory rights under the Consumer Rights Act. That would demand that the vehicle be of a satisfactory quality. The definition can be found here
but I think most courts would accept that a fairly new car would not be expected to have a fault of this nature unless the purchase price was extremely cheap.
The reality though is that if they refuse to repair then your only option is to have it done elsewhere and sue them for the cost. You would need to warn them about your intention to do that though in advance.
Can I clarify anything for you?