B737 Captain reported receiving conflicting information from multiple departments regarding whether dangerous goods were loaded on board prior to departure. After extensive delay and a lot of back-and-forth; it was finally determined that no DG had been loaded on board and the flight took off.

Narrative

We were late pushing due to mechanical. After that was handled with poor communication from Maintenance we were ready to go. Just before push; a Ramp Personnel came into flight deck with a large piece of paper that I assumed was the fuel sheet. I looked at the fuel and told the man 'we're good' and he left. Then I looked closer at the paper; and it turned out to be a dangerous good notification that I had never before seen. I asked Operations if we really had DG (Dangerous Goods) on board; they said yes. I texted Dispatch to verify and ask for ACARS DG notification; Dispatch said we did not have DG planned. Dispatch verified with Load Planning; they said no DG. I asked Local Ramp and Maintenance; including the ramper that gave me the paperwork; they didn't know. I asked Operations again; they finally verified we had no DG onboard. We pushed back and we're halfway to the runway when ATC said company is trying to get ahold of us. We parked and called Operations; they said to come back to gate so they could secure DG in our pit. I asked that they verify again that we actually had DG onboard. We waited about 20 minutes; then Operations said we did not have DG. We then elected to taxi to the runway and take off. Flight to ZZZ1 was late but uneventful.