I have bought a timeshare or a holiday club membership
As long as the message has been sent before the cooling off period has expired, the cancellation is valid. If the trader has an e-mail address, an e-mail might be enough. It is, however, important that you save all correspondence with the trader, in case you need to provide proof afterwards, that you have cancelled the agreement.
If more than 14 calendar days have passed, the cooling off period might still apply. According to the law, certain information has to be provided from the trader at the time of the sale and if you have not received the information the cooling off period is prolonged.
Read more in the article Timeshare & holiday clubs