Back in the early ‘80s my wife and I toured Europe and my wife bought some crystal items to bring home. A couple of weeks after we got home we started getting letters and even a phone call from the shop where she bought the crystal. Apparently, they had forgotten to collect the VAT. Since we never heard of a “VAT” and couldn’t get an understandable explanation of what it was for from the guy who called us, we just laughed it off.
You would be exempt from paying the VAT, but I suppose since you and the store didn’t fill out the appropriate forms before you left the country, the store probably got left holding the tax bill.