Stealing My Money Back From the Banks

Is a small amount compared to the trillions of pounds they have sucked out of us, but yesterday when I was paying £110 into my bank, I got a receipt from the machine for £130 having been deposited.
What will I do with my massive windfall? I think I will wait until they annoy me over something trivial then take them to the small claims court for the shoe leather I wasted in going to see them.