Yes... It happened AGAIN! I contacted the shop as soon as I found out and they removed the t-shirts.They apparently bought the fabric from a manufacturer, without knowing it was stolen. When I asked if they could give me the name of this shop, they unfortunately completely ignored my question.
It's more than probable that other shops have been using this fabric.
I'm just thankful that someone recognised my illustrations and was kind enough to let me know.
But why does it happen so often? I wonder if those are the same people who stole my cat pattern a few months ago. They sure are making money out of my work!