Claiming money back from a door to door salesman

A sales agent recently came into our house (around 7 pm) to do a demonstration on an expensive vacuum cleaner. After several hours, my friend and I decided to take 1 unit each because they have offered an instalment payment scheme for 18-24 months.

The following morning at around 10 am, I tried to call the agent and sent him a message that I don't want to proceed with the purchase as my husband did not agree to it.

He is telling me that I can return the machine but I have to pay AED 4,000 contract cancellation fee, claiming that the machine has already been registered internationally under my name and the fee they are asking is for the cancellation.

I did not even open the machine and notified him in less than 24 hours and now I have to pay AED 4,000. Is it right for them to write in the contract such terms on the cancellation?

Also, they refused to take back the machine until I have given them full cheques for the AED 4,000 penalty.

Thank you