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You need to contact your Title Insurance company. This was the company that insured you against things just as these when you bought the house. You should have been given a copy of your Title at closing or your real estate agent or the attorney who did your closing when you bought the house should have these. You need to contact the Title Insurance company and bring it up with them as it is their responsibility to pay for things like this if they indeed insured for it (and it is customary to do so unless something strange happened for your closing). This is really the proper recourse for you. Contacting the previous owners isn't really going to help a lot since the Title Insurance company has to do this and you pay for this at closing for them to do this.
If you find out you don't have Title Insurance or they don't insure against it, I would sue your attorney or real estate agent because it is their responsibility to let you know about things like this but I think you probably do have Title Insurance and they need to take care of this.
If you did not get Title Insurance when you bought your house, you will not be able to get Title Insurance now. However, if you had an attorney do your closing, there is a very good chance that you received Title Insurance as it is very rare when Title Insurance is not obtained when buying a house.
If you do want to try to sue the seller or the attorney or agent that helped you buy your house, go to your local courthouse or do a google search for it and go to the Small Claims Division. Ask them about the dollar limit that you can sue for and then they will show you the forms that you will need to fill out to file a Complaint and to Serve whoever you are trying to sue. Then you will need to pick a hearing date. Once the hearing date is set and you have sent notice to the people you are suing, they will have a chance to respond and then there will probably be a date where both of you can come back and let the Judge know if you have settled the dispute. If not, then the Judge will set a trial date. The clerks at the courthouse should be very helpful at letting you know exactly what forms you need to fill out. I would encourage you to obtain an attorney, possibly one that works for free or a student at a law school in your area, to take your case. Many times, law school clinics or law clinics will help you for free. I would take a phone book and just look for some of these attorneys as this will increase your chance of getting something back.