How to revoke a Tax Declaration?

during the 1980's cadastral in our place , our unregistered land which we have an open, continous possession since 1975 was divided into 2 lots. Lot 3254 named after my mother and Lot 3258 named to another person.

Upon checking the history of Lot 3258 we found out that it was declared new in 1994 and was issued a tax declaration in the name of another person not my mother. Since my mother did not sell any portion of our land we decided to consult the municipal assessor about this. I ask them what are the legal papers and other supporting documents did the person whom the new Lot 3258 declared submitted in order for the assessor to issue a tax declaration of the said newly declared Lot? The assessors answers is none and further stated that they only copied what is reflected as cadastral claimant reflected on the cadastral documents they obtained from DENR without even verifying as to how he acquired the land. The assessor also mentioned that they based the issuance of tax declaration on the result of the tax mapping in our municipality. This is realy a big question mark for us because until now we still possess Lot 3258.

The problem now is we tried to have our land titled and we could not because a new lot was created and named after another person.

what are the legal procedure and basis to revoke a Tax Declaration?

keep digging further into the history of how the tax dec info was created. if it is just an error then try to get the DENR to correct this.