Cold callers are not just a nuisance but if you subscribe to the TPS (telephone Preference Service) they are acting illegally and should be reported to TPS, where you can file a complaint on its website https://complaints.tpsonline.org.uk/Consumer/
Make sure, of course, that you take a note of the company name and the date and time of the call.
No reputable timeshare company, and certainly none within RDO membership, will ever make an unsolicited call to you and you can be confident the company is trying to obtain money from you without providing a meaningful service in return.
Mindtimeshare.com, which provides an enforcement service for RDO, taking action against companies that target timeshare owners, has published an extremely helpful list of companies that have been cold calling timeshare owners over the past year. This list can be viewed here