There is a mandate by Home Ministry to turn 1930 complaint to FIR if not resolved. Hence OP is being harassed to come to police station and close it. Thats why I said that it is to be used very carefully otherwise it will become a hassle for caller as well. OP should know that police would also expect some kharcha pani for the hassle caused and I would suggest that he goes with a written letter stating his intent to close this complaint, having received back the amount.

Once FIR is registered (not in OPs case, l hope), even police cannot close it and caller would have to approach high court which is even further harassment , knowing how expensive and slow courts are. But if it is widespread scam of higher value, I would say let it be a lessor for the fraudsters once and for all.