Somebody claims that our lot has been sold to them-now they want us to moved within 15 days? Any Advice???

You received what is known as a demand notice demanding you pay what is owed (the whole loan amount) immediately or you will lose the property. If you can come up with the money you can keep your lot by going to court, but if not you must move. This is what happens when you miss payments. Apparently it just took them a long time to process the issue in the Philippines.