Complaint against a Language School in Brussels

I have registered with a Dutch language academy last week for a 5 classes course on Saturday. The class was not on par with what the course description on their website shows.

So after finishing the first class I emailed them that I wish to cancel my enrollment and pay for the first class and material and requested a refund.

After 2 days of no response, I follow up only to receive that they don't refund and that I have to be specific with what my expectations are! This is not the first language course I take, I have taken one at Atlas and online with a private tutor. After explaining that to them, they literally responded: The other students are quite happy with the course perhaps I need to go to a lower level...

At this point, I decided to contact the academy directly and speak to the manager, who was very rude and I was quite frustrated by how adamant she was on not acknowledging if a customer is not happy with the service they should not be forced to continue with it. I was angry and every time I expressed my frustration he would simply respond with No we are not going to give a refund, then she literally hung up the phone on me.

What a rude and poorly customer-oriented establishment and staff.

I would like to know where I can file a complaint against them under consumer rights.