I think you are right, Rodolfo. The writer should have said "If you have any questions,.." or "If you have any queries..". I suspect that the writer was a native Portuguese or Spanish speaker, and that they were influenced by their first language. "Doubts" sounds like the wrong word to use in that context.
In fact, if I were in your position, I would have some serious DOUBTS ( apreensões) about this language course. If you have doubts about something, this means that you're suspicious about it. If there are English language mistakes in the promotional material, I really wouldn't trust this course. In this case, you really should have 'doubts'..... but that isn't what the writer had in mind!