Language school refuse to pay refund

My cousin (from a third world country) applied for a visa to attend a language school in Frankfurt, but his visa got rejected. The reasons given were that his motivation letter was too weak and that he hadn’t started learning the language yet.After the rejection, he informed the school and had to return the original enrollment letter. It sounded like he would get a refund. However, now the school is refusing to refund him, saying that the visa rejection is not their fault and that he can join the course online instead. The course he paid for was supposed to be in person. As far as I read in terms and conditions, there is nothing about visa rejection. Once I asked the staff in person, can he get refund when his visa got rejected and they answered yes ( but no evidence ) . It's 3300 Euro and it is a big amount for him. Can someone advise or guide us how should we do?