Scottish Power

I recently left Scottish Power, I was due a refund of £72.32 but instead they took a further £27.68 rounding up the money they owe me to exactly £100. When I called them they said I needed to sort that out with my bank through the direct debit guarantee scheme, they then said all they owed was £27.68 and then they cut me off. Smells like fraud to me, a fairly small amount but if they do this to 10,000 customers they have £1,000,000 in their accounts that they have obtained by illicit means. I intend to send them a formal demand for the money they owe and then will take court proceedings followed by a wind up order when they fail to respond. They are a shameful and incompetent company.