A320 Captain reported having to return to the gate as the dangerous goods were loaded and documented in an unaccepted format.

Narrative

During preflight we had received a Planned Dangerous Goods (DG) Summary; so prior to pushback we expected to receive a Final DG Summary. The push crew contacted us via intercom advising they were ready for brake release and pushback. I told him we could not push back until we received and acknowledged the Final DG Summary and asked him if it had been sent. He said he would ask his Ramp Lead. After a couple of minutes; I asked again and he said they were working on it. I asked if the DG had been loaded and was told yes; it was loaded. At that point we sent a report DG message via ACARS and a Final DG Summary" printed out. Not realizing this was not in the currently accepted format we sent the DG acknowledgement code message acknowledging receipt of the Final DG Summary; requested pushback; and advised the push crew when we were cleared to push. After pushback and engine start; we were advised by Ramp Control to return to the gate. We were told Load Planning was not satisfied with the way the DG had been loaded and documented so they opened the forward cargo pit and removed it. After reviewing the latest pilot bulletin related to DG; we realized the format of the final summary message we received was incorrect."