FLC OF AN LGT CHANGED TO TWR FREQ BEFORE INSTRUCTED BY APCH AFTER BEING CLRED FOR THE APCH.

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VECTORING INTO O'HARE INTL WE WERE CLRED FOR ILS RWY 22L AT WHICH POINT WE CONTACTED TWR CTL ABOUT 12 MI OUT. AFTER NUMEROUS ATTEMPTS TWR TOLD US TO GO BACK TO APCH FREQ. ON INITIAL CONTACT; APCH EXPLAINED TO US THAT THEY TRIED CONTACTING US 4 TIMES AND THAT WE SWITCHED FREQS TO EARLY. THEY THEN POINTED OUT TFC THAT WAS ALSO CLRED IN FRONT OF US ABOUT 3 MI AHEAD. WE PERFORMED S TURNS TO THE R TO GAIN FURTHER SEPARATION AND THERE WAS NO FURTHER INCIDENT. I FEEL APCH CTL HAD NO BUSINESS CLRING US FOR AN ILS APCH IF THEY WERE PLANNING ON TURNING SOMEONE IN FRONT OF US. WE WERE NEVER TOLD TO STAY WITH APCH CTL OTHER CREWMEMBERS FELT WE WERE TURNED OVER TO TWR ONCE CLRED FOR THE APCH. THE SPD OF COM WITH ATC AT O'HARE INTL ARPT IS UNNECESSARY AND CREATES MORE PROBS THAN NORMAL. WE DIDN'T GET AN OPPORTUNITY TO CLRLY REPEAT OUR INSTRUCTIONS BECAUSE BOTH APCH AND TWR JUMPED ON TO THE OTHER ACFT. (IT WASN'T THAT BUSY!) TWR ON INITIAL CONTACT SHOULD HAVE BEEN ABLE TO TELL US ABOUT THE OTHER ACFT INSTEAD OF TELLING US TO RETURN TO APCH CTL. AFTER ALL WAS SORTED OUT; APCH TOLD US EVERYTHING WAS FINE AND IT WASN'T A PROB.