Charging more than advertised! Violated customer

No Stars! I am so disgusted, I purchased 3 online courses via Udemy.com on a alledged 90% discount advertised. Upon purchasing, charged incorrect amounts for all three! Upon contacting support, I was told that they cannot do anything because their system says otherwise despite me sending proof of the incorrect transactions with their company NAME! The support consultant, Mario Turcios, tells me he cannot do the partial refund of the over charged amounts and suggests that I made an error. My account is made less that I committed to paying, and no actin is being taken on the violation of my consumer rights.