If they don't login and chargeback, that is a refund request done poorly. They never took possession of the course.
You should have a refund process in place so refund requests don't become de facto chargebacks. That would reduce your chargebacks and protect your merchant account.
Here is another crazy idea, ASK PEOPLE WHY THEY ARE CHARGING BACK!
Don't assume they are scammers. They might think you are shady, they changed their mind, the course is not as advertised, delivery is poor, logins don't work, your biller name on their statement looks scammy etc
When you assume ...