[steffib]

First, if you want to make the strongest possible argument for your case, I feel it would be better to post this in the appropriate place as Bea pointed out, and not in the swap meet.

Second, from reading the message, I suspect that there may have been communication problems, which as a non-native speaker myself, I know all too well. It may be a good idea to write down all details, amounts, orders, dates, and come up with what you would like the vendor to do to make this right. Then have a native speaker (a dancer friend who is a lawyer would be ideal) with that information in hand call the vendor and tell them firmly and politely what problems you encountered and what you'd like them to do.