I know he has a set price in his contract but still, it's not like Atletico is the only club that wants him. Other clubs are probably willing to pay more for him. Cadena probably isn't reliable, never heard of it so I can't imagine it is .
The price that is reported is absolutely ridiculous, I don't think Dortmund would sell him so cheap. Sure Atletico is a big club but so is Dortmund imo, it isn't that big of a step up.