you may need to change more than the title
Just changing the title does not always work. CL filters are getting better and better at finding duplicate ads. You should come up with two or three really good ads that are different, but represent your property well. Re-order paragraphs, etc. And then add pictures and a link to the property.
Sign up for an account and use it to manage and repost your listings. It's VERY easy to do this when you have to repost every so often. And be PATIENT.
Also..... don't post on the Mexico City CL. Pick cities where you think your customers will live, pick cities where there are inexpensive direct flights to your destination, etc. For example, in PV we see a lot of people from the Bay Area, Seattle, Portland (Alaska/United Flights are easy), Phoenix (US Air flies direct), Denver (Frontier) and Dallas & Huston (American flies direct).