Rude with a side of hairy cake!

I ordered a slice of cake, only to find a nice long black hair baked inside!! After finding this, I was offered a replacement slice, (which is to be expected after finding that). When it came to the bill, it would be expected that I would not be charged for this slice of cake as it was their hygiene that was not up to standard. When asking the manager about this, she first said she did not understand what I was saying and then argued with me and rudely stated that I received another slice to make up for it. I did not receive an apology let alone have one slice of cake removed off the bill. I find this to be poor customer service and I would expect a manager to at least apologize for something highly unappetizing especially when making me pay for it as well. After arguing with me, she turned around and just walked away. When broaching the matter in a polite way, simply enquiring why I would be charged, she responded in a very rude manner.