GTR32G is basically right.
They don't have to show you quotes if done through insurance. Unfortunately, you're only argument is that "The bill is too much and you want it reduced". Proving the battery isn't even in the boot should basically give reasonable doubt to the bill. Then try and get things removed from their.
ON another note, someone mentioned bankruptcy... NEVER EVER think of doing this. If f**ks you for 8 years royally. They will remove any existing credit, and then you stand little to no chance of getting it again for at least 8 years, very possibly even longer. (that's credit cards, debit cards, home loans, personal loans, 'buy now pay later' finance, phone plans, EVERYTHING becomes a major pain in the arse)