ReactPlus - ******** service

I purchased a device from the Istore and was advised that ReactPlus is offered for free for 6 months. I downloaded the ReactPlus app to see what it entails and a few days later after downloading the app I deleted it I did not require it. I now receive an e-mail advising that I shall be automatically billed for a monthly subscription for the ReactPlus and I am advised in the e-mail to cancel and opt-out via the ReactPlus app. However, I no longer have the ReactPlus app and there are no details on how to cancel the automatic subscription. This matter shall be referred to the National Consumer Tribunal for investigation.