UNAUTHORIZED RWY ENTRY BY CORP ACFT.

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WE CALLED ATC FOR CLRNC AND WERE GIVEN IT IMMEDIATELY. WE WERE BEING RUSHED BY ATC AT ALL PHASES OF THIS TRIP! CLRNC WAS GIVEN QUICKLY AND WE WERE ASKED IF WE WERE READY TO TAXI. WE SAID YES AND WERE TOLD TO TAXI TO PAD AREA OF 27L AT ORD VIA THE CARGO TAXIWAY. WE WERE CONTINUOUSLY GIVEN DIFFERENT INSTRUCTIONS AND TOLD TO MONITOR DIFFERENT FREQ. THERE WERE AIRLINERS ALSO IN LINE FOR DEP. WE ARE FLYING A NEW AIRPLANE AND ARE NOT USED TO THE NEW TAIL NUMBER SO THIS ADDED TO THE CONFUSION. WE WERE CALLED BY WHAT I THINK WAS AN MLG ACR ACFT WHICH ALSO ADDED TO THE CONFUSION. WE WERE TOLD TO TAXI INTO POS AND HOLD ON 27L. WE DID AND WERE STILL ON GND FREQ. WE WERE THEN TOLD TO DEPART IMMEDIATELY SO WE DID. I'M NOT SURE WE DID ANYTHING WRONG; BUT I FEEL THAT WE WERE RUSHED BY ATC INCREDIBLY AND TO TOP IT OFF; WE WERE AT AN UNFAMILIAR ARPT; AT NIGHT AND IN A NEW AIRPLANE (NEW TAIL NUMBER). SUPPLEMENTAL INFO FROM ACN 202556: ATC SAID TO TAXI TO THE 'PAD' VIA THE CARGO TAXIWAY. THERE WERE MANY OTHER ACFT IN THE AREA AT THE TIME AND THE PF WAS SOMEWHAT CONFUSED. WE WERE TOLD BY ATC TO 'MONITOR' FREQ AND SO WE DID. THEN WE WERE TOLD BY GND TO TAXI UP TO BUT HOLD SHORT OF THE PAD; I THINK. NOT BEING FAMILIAR WITH THE AREA AND BEING RUSHED BY ATC; WE TAXIED ONTO THE 'PAD.' GND THEN SAID SOMETHING; AND AN ACR PLT GOT INTO THE CONVERSATION. GND TOLD US TO TAXI INTO POS AND HOLD. WE DID AND WERE TOLD TO SWITCH TO TWR. HE TOLD US TO TKOF; BUT HE SOUNDED MAD. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR GAVE INFO ON STARTING POINT AND TAXI RTE VIA 'CARGO' TAXIWAY. PRETTY SURE THAT GND CTLR GAVE CLRNC INTO TKOF POS. FREQ CONGESTION WITH CTLRS TALKING CONTINUOUSLY AND AT HIGH RATE OF SPEECH. DOES NOT THINK THAT THEY DID ANYTHING WRONG BUT WERE VERY CONFUSED AND MAY NOT HAVE COMPLIED WITH ATC INSTRUCTIONS. ACR ACFT MENTIONED IN RPT WAS PROBABLY THE ACFT THEY SAW TAXIING TO THE SAME RWY ON THE PARALLEL TAXIWAY. NOT SURE WHAT ACR SAID ON FREQ. BUT IT WAS DEROGATORY REMARK ABOUT RPTR ACFT ACTIONS.