AITA for telling my BIL to pay me $700 for my lost coat when I bought it for $100?

I was at a mall with my fiancé last weekend when I found this coat I loved. It was a bit on the expensive side, but it was the exact coat that I had been looking for, so I decided to treat myself. I paid $100 for the coat in full when I bought it. I wore the coat out of the mall, and when we got back to my fiancé’s brother’s house, I took the coat off and put it in my room. The next day, I went to look for my coat to wear to work, but it was gone. I asked around and nobody knew where it was. Then, I remembered that my fiancé’s brother and his friends love to joke about stealing women’s coats, so I asked them if one of them had taken my coat as a joke, and they all just laughed. <br><br>My coat was very expensive, so I definitely missed it. I asked my fiancé how he’d like me to replace it. He said he’d leave it up to me, but he thought we could just forget about it since money is tight right now. I told him that I spent that money, and my late grandmother had saved up and given me the money to buy that coat. So, I can’t just forgive it. He asked me to ask his brother to pay for the coat, but I didn’t want to ruin Christmas. So, I told him that I’m fine paying for the coat out of my grandmother’s money since I have a few more weeks of paying off it before it’s paid off. <br><br>However, my fiancé said sure he’d leave it up to me, but then later asked me if I could just pay for half of the coat. I said no, I would pay for it all. He then asked me to just ask his brother to pay him half of the coat and he’d pay half. I said no again, then he asked me to ask his brother to pay me $700 for the coat since I got the money from my grandmother. Now his brother feels offended, and he thinks I’m being a stick in the mud about it. So, AITA?<br><br>(Note: I am from the Carribean. Some of the words may not make sense, and the spellings may be incorrect since I’m on my phone)