Cancellation not permitted

I canceled my order via their website on the same day, within the hour, of ordering. This was on the Saturday. I received an email on the Monday saying my package will be posted in 2-4 days - making Wednesday the earliest it would be sent. I confirmed the cancellation two more times on the Mon and Tues by replying to their email. I also stated that I had already canceled the order via the website on the same day as ordering. I have received a reply today (Wed) saying that the package has already been dispatched and therefore I cannot cancel. I canceled three times within four days of ordering and before the earliest they confirmed posting would take place. They are ignoring this and not honoring what their policy states on their website and the timelines given in their email. It is extremely disappointing.