I would say goodbye to this guy right away.
PADI or any other agency that he teachs thru would not be happy to hear of what he is doing not to mention his Insurance company.
Keep on your bank! Even if they say they cannot help insist they call Visa Or Mastercard (assuming you have one or the other) as they have certain policies that must be followed also.
Its a shame that it is dive shop owners like this give a lot of the others a really bad name. I almost never got into diving after shopping for a mask to do some snorkeling and got nothing but attitude from the dive shop I was in, I figured they would have been happy as I was looking at a 75 dollar mask, but no nothing but crap from them. Thankfully I went to another dive shop and found some really helpful people. Oh and the shop I went to first, They went out of business about 10 years ago, GOOD RIDENS.