Hi There!

I have been going to the same panel beater for 5 years. I have been pretty unlucky with my cars lately (not my fault except for the last time) and this guy has seen me around 6 times in that time. I would estimate 10-12K from my insurance company.

He provides loan cars, a must for me, and each time we have had to sign a bit of paper to say we accept liability etc, and that we would need to pay an insurance fee of $15 + GST per day of loan. My wife and I have both had our cars in and never been invoiced for this amount.

My last repair was major and it took him 41 days to repair the car which included an extra week and a bit for parts since he didn't assess it properly for damage and needed more 2/3 of the way through.

Today I have gone to pickup the car and been given a bill for $700.

He is saying he won't back down and I need to pay it.

My arguments against it:

1) We have never been charged before, creating an expectation we were exempt for some reason
2) We were not told that this time would be different from any other, therefore leaving us unaware we would be charged.
3) Had we of known I would have chosen to supply another car myself (a much better one at that) or taken the car to another location that doesn't charge these fees. I called 3 at random today who don't charge. 
4) $700 seems ridiculous to me for 41 days of insurance cover, I know that my car, which is likely in excess of 10x as valuable and is insured for commercial use, is only $500 more per YEAR.
5) He originally estimated a fortnight for the repair.


His argument

1) I signed to say I'd pay it.

The complication is that I left my sons stroller in the boot of the car, and he is saying he will not allow me to collect it until I pay the outstanding money. 

 
What should I do?