Do Jasoos (1975)

Two bumbling, middle-aged private detectives, Dharamchand and Karamchand, are assigned to locate the missing daughter, Asha, of a multi-millionaire. Their adventures take them to a gangster named Prem Chopra and a criminal don named Motilal Sippy. With a lot of skill, action, and fights, they do rescue the girl in their captivity, and bring her to her dad. It is then that they find out that the real Asha is already back home safe and sound, and they had rescued the wrong girl. But now it is too late, as the underworld and it's men are out to get them.