A321 Captain reported confusion on whether DG was loaded onboard and after confirming with Operations there was no DG on board; pushed back and began to taxi to the runway. However; while in queue for takeoff; Tower informed the flight crew to return to the gate as DG had actually been loaded onto the aircraft and needed to be removed.

Narrative

Sitting at the gate preparing for departure and a NOTOC advisory was printed from ACARS. Around pushback time; I assumed that the Crew Chief may not have known that we needed Dangerous Goods (DG) paperwork. Trying to mitigate a lengthy delay; I called Operations on the radio and asked if they could clarify. A few moments later Operations informed us that DG was not loaded onto the aircraft. I sent Dispatch a free text via ACARS to advise them to plan on the Crew Chief cancelling the NOTOC. Dispatch thanked us for the heads-up. About one minute later; a NOTOC cancellation was received via ACARS. We pushed back a few minutes late and received a load close-out that confirmed no restricted articles were loaded onto the aircraft. We taxied to Runway XXL with no issues. While in queue for takeoff; we received info from the Tower that company wanted us to return to a gate at the same time we received a message from the ACARS printer that DG was actually loaded onto the aircraft and we needed to return to a gate. We returned to Gate XX. A Supervisor informed us that the DG was loaded onto the aircraft and confusion from the ground crew on whether it was actually loaded had taken place. The DG was unloaded and we departed without further issue after waiting about 30 minutes for a new load close-out. Unbeknownst to the Captain and I; we had inadvertently pushed back and taxied to the departure runway with the intent to take off with DG onboard without a NOTOC in our possession. I'm not sure if the factors were with the Crew Chief or the cargo facility that deals with DG but it appears that technology or improper hazmat placarding may have contributed to this error.