well somebody is making something up
you 'phone' an organization...prank or not..known for aggressively proselytizing...and then express surprise that they aggressively proselytize...if that is what is happening...the language about you volunteering to be a jw just does not ring true...so either you are making the whole thing up...or your friend is
if you told them that you are doing a school project then they will not be hunting you down..they will either believe you or will think you were just someone having a laugh
you are not the first person to do this..and sure an effort will be made to see if you are genuine..but the fact that you did not give your address..and that you are aware of how to contact them..will allow them to believe that if you are for real then you will get back in touch
if they ever come to your door...because you gave your name or because they are just doing regular house to house visits then all you do is tell them you are not interested and they will not bother you..
unless of course you are interested..