How can I return a faulty laptop?

I recently bought an Inspiron 7640 direct from Dell online in the UK. When it arrived I was not happy with it and wanted to return it but I was told that I couldn't as I had bought it for business use ( I am a sole trader). I was offered the opportunity to buy a different charger so as to free up the sole USBc port for other uses and I decided to make the best of it. I then left the country for 28 days and on my return began to set up the new laptop. However there is a fault with the cursor so I cannot type on it. The cursor jumps all over the text and deletes it spontaneously. Technical support has not been able to correct this problem, and of course the system is completely useless to me unless it is corrected. I would like to return the machine as not fit for purpose but I can find no-one to contact and no way to do this as it is now more than 30 days (or 14 for business ) since the machine was delivered. Can anyone advise me?