FNB ******** charges to their customers

I recently made a purchase on my card to a well known accommodation platform. I have made several purchases on this platform in the past. However, to my surprise, FNB went and charged me a further amount of R81,40 which was never known to me. They did not inform or warn me about this charge, they just simply helped themselves to my account and took an extra amount off. This has never happened before on the accommodation platform, and it seems FNB is doing exactly what they want with my account. I want this amount credited to my account - it is so disgusting how FNB just ***** from a person, is this normal?