Money ****** from account after cancellation months ago

After a really good experience with this company. I discovered a few days ago that money was ****** from my account after i had cancelled my subscription in October 2017. It is really worrying that they were able to debt my account and still had access to those details. Now they say it is going to take up 10 days to return the money? They manage to take it easily? Why does it take so long to return. There cancellation processes are pretty flawed, so why are their return policy's so good that it takes 10 days? Do they do this to accumulate interest on their accounts? Why don't i get the interest they make off my ****** money when i get the refund? Because i would of had interest made if they money was still in my account. Oh wait i cannot make interest now because it was ******.