Direct Energy Regulated Services Paying off statement via Bank; returned my payment and claiming I didn't pay the right company (I used the accound # on the statement) charged me a late fee. Edmonton, Alberta

I made the horrible mistake of signing up for their fixed rate service back in October '08. They gave me 10 days to think about it. I got my bill in January and it was triple what my previous bill was. We decided after 2 months of horrifying bills to cancel this service, and decided to just eat the $400 cancellation fee. The first time we tried to set up a payment plan (since we couldn't afford to pay them $400 in one shot) they hung up on us. Finally they let us pay $100 until it was paid off. On Saturday I didn't think I could mail in a check on time so I went to TD to pay it, using the blue statement with accound number printed on that statement. TOday I get a refunded cheque say I'd overpaid one account. I call DE and they said I'd paid the wrong company. I asked If I was getting a late charge for this and they said yes. To be clear I USED THE SAME ACCOUNT ON THE BLUE STATEMENT THEY SENT TO US!!!!! But they are claiming I didn't pay the right company. Is this legal?  This just seems so fishy!