So, I got a pizza for free lol!

I ordered Domino's pizza earlier. I placed my order through the website online. It was for delivery. It wouldn't let me place my order the first three times, so I was going to give up and call instead. I refreshed the page, and I tried one more time before calling. The order finally went through. I received my pizza, and then I checked my card. I left a 15 percent tip and paid 20 for the pizza, so I thought. Turns out, it was a glitch. They never charged my card. I don't have a pending purchase either. I am now trying to decide whether I should call, or just take it lol. There was a time when they charged for an order and didn't show up. So, I am at a loss. I want the driver to get a tip (I used to be a server), but I am also happy I got a free meal.