A fast one on customers

I bought a voucher for 10 sessions for my son at the course at Mall of Africa. When I wanted to redeem the vouchers later, they told me they don’t use a voucher system. I sent them the proof of payment and emails confirming that I had indeed bought vouchers. I requested that they refund me. They are now not returning my calls and WhatsApp messages, and are clearly not planning on refunding me.