Creating a sell or buy order does not mean you get it all filled. There can be partial fills, in that case you would still have open orders with the difference.

You can check your open orders under „My Orders“ or „Open orders“ under Account.
There can be unlimited fill orders per buy/sell order but also none when nobody on the market fills your order.

I think our support was not fully informed about this either, but as they say, it’s a misunderstanding.