Impossbile to cancel iStore pre-order

I pre-ordered an item on the myIstore website on 27 January. When placing the order the expected date was mid-february. Two weeks later when I check up on my order the expected delivery date has changed to mid-march. I then decided to cancel the order as I the product is available on Takealot for delivery within 2 to 5 days. When using the live chat facility to cancel I was informed that I need to send an email to request cancellation. I send an email and got no response. I then called their call centre and they said that I will get a response within 24 to 48 hours. It is now 48 hours later and no response