Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Confusion; Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Taxiway
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance
Human Factors; Procedure
We were on the ground in PIT after push back from the gate. Ramp gave us taxi instruction V5; V; hold short of E; then contact ground. FO switch FRQ to ground 121.9.  Ground told us; 'we never gave you the instruction to taxi.'  We told ground we were given taxi instruction from ramp and ramp told us we never gave you the instruction to taxi. We told ground we were given taxi instruction from Ramp and Ramp told us to hold short of E then call ground. Controller told us to turn right on Delta and hold short of W; you have a wheels up time; then controller came back and gave us the number to call. I did call the number; controller told me; 'We'll listen to the tape and then take the appropriate action.'
My CA and I were very surprised by this response as we had followed taxi instructions and our aircraft was the only aircraft taxiing/moving on the south side of PIT at that time. There was no danger to our aircraft or any other aircraft whatsoever. The south ramp; taxiways and runways were completely free/empty of other aircraft operations at the time. PIT was using 10L for arrivals (10C for departures) at that time.
Captain reported being told specific taxi instructions to a runway by Ramp Control. The crew taxied as instructed then contacted Ground Control. Ground informed the crew that they did not have clearance to taxi as they did. Flight crew then received different taxi instructions from Ground and were given a phone number to call.  Pilot called the number and was told they would look into it.