Fly.cool failing custom services

I have been customer to Fly.cool for the past two years, I decided to end my relationship with fly.cool on the 24th of May by sending by WhatsApp as their monthly subscription were becoming affordable for me. They agree to cancel my internet services with and committed to not making further subscription deduction from my bank. Fly.cool usually deduct the subscription amount of R389.99 on th 26th of each month, on the 26th May Fly.cool want ahead deducted the monthly subscription after promising it will not do so. I tried contacting them several times to let them know, request for a refund but until today a month later I still have not received the refund.