how do I make a cancellation of my premium contract
I had the same question: you can't edit your payment/account details via admin - instead, there should be a separate link contained in your email which you received when you signed up!
Hi, In the admin part when clicking on "Edit" right to "Premium",you can read :
"Kindly contact us at: email@example.com to cancel subscription anytime."
Have cancelled it for you.