1. FMB alone is not the records to determine the easement rights, the pathway what they refer to as a right has to be established by them by documentary evidence. If this proeprty was under your possession and enjoyment for 30 years or more and nobody had passed through them nor had claimed any rights for easement so far in all these 3 decades, then they cannot force you to open the fencing. If at all they have any rights they have to prove them through court of law and not through the village or taluk revenue authorities. But the FMB records are not any documentary evidence to prove your statement too, in fact your voluntary act of obtaining the FMB in your favor may have an adverse impact to your own defence.
2. The FMB is not the authority to determine your rights or denying their rights for the pathway, If they want to conduct survey,.you may allow them by taking notice and record your objection to the survey work.
3. File an injunction suit to restrain them from interfering in your possession and enjoyment of your property