If money was accidentally put into your account. Would you inform your bank for the mistake?

I had this once happen to me. It was money from a company that got on my nerves. I went to this site and ordered two different coffees. The company said it was free and I had to pay $3 just for S&H. Nothing on the site including terms mentioned anything about being sent 6 boxes of coffee two weeks later that will be charged into my account. So two weeks later I randomly get a huge box with 6 coffees inside. Inside the box a statement that my account has been charged $40+. I called the company and told them I didn't order any box and I'll return it to them in exchange for refund. They told me I could keep it and they won't give me a full refund. It turns out they never charged me the money in the first place...but they still refunded me for money that wasn't charged. I didn't bother calling them they mistakenly refunded me cause they already got on my nerves before. That's all. The company is Gevalia and there's so many complaints from people just like me online.