Clay Cafe Hout Bay - no responsibility taken

A few weeks ago we visited the Clay Cafe in Hout Bay to celebrate a friend's birthday. My husband and I each painted a mug. We were very excited to see the results, but when we collected them a couple of weeks afterwards we were very disappointed with the result. The charcoal paint that both my husband and I used on our mugs had blistered/bubbled all over. When contacting the Clay Cafe, we got a non-committal response, saying that the painting technique we used was incorrect. According to them the blistering occurs when the paint is app**** too thickly. The first problem with this is, that the guy who came to explain/demo to us before we started painting, was very specific that we had to put AT LEAST 3 layers of paint on. Being strict rule followers, we proceeded to do just that. If this is a common problem, you would think that their instructors would be certain to point that out. The second problem is the blistering occurred on more than just one person's mug (it's unlikely that both of us used the same amount of "incorrect thickness" painting technique). We did some research, and it seems more likely that the paint was contaminated, as the charcoal paint we used was in a different container than all the other paints (being a ***** top container, opposed to the other ones that had flip tops). We assume that the paint had spilled and that someone had just sc****d it up and put it in a new container. But the Clay Cafe is taking absolutely NO responsibility. (this after querying with them twice).