Unable to Cancel Ewa Premium Subscription and Prevent Future Charges

I purchased an Ewa Premium subscription via Instagram and I am having difficulty cancelling it for the future period. Today I tried to cancel my subscription so that it would end in 3 months’ time, but the system did not allow me to clearly set this and I am worried that I will continue to be charged after this period. Up to now I have been charged £30 for the subscription. I contacted support about cancelling and ensuring there would be no further charges, but I still do not have clear reassurance that my subscription will definitely end after the 3‑month period and that no additional payments will be taken. I request written confirmation that my Ewa Premium subscription will be closed at the end of the 3‑month term and that there will be no further charges after this period.