BE33 Pilot reported the aircraft door opened shortly after takeoff. The pilot described the difficulty communicating with ATC that the aircraft had just taken off and the need for an immediate return.

Narrative

Experienced in-flight door opening due to malfunction of the door latch strike plate 30 seconds after departure passing 1200 ft. on Runway XXR. Initiated a 180 deg turn back to ZZZ. Attempted to contact our initial controller on 125.70 that we needed to return to the airport he became confused and did not know who we were and had us 'ident' and then became distracted with other traffic in the area and never called me back. By then I was south of the airport and Runway XXL was a better option for a safe landing and I contacted the south pattern frequency of 119.20 since I had no reply from 125.70 and she was not too happy about me being on downwind now and let me know. that 'I was in the ZZZ Class D without a clearance' although we never did leave the ZZZ Class D airspace because the door popped open just after take-off. From there I was cleared to land Runway XXL and contacted the tower and then called ATC after landing. I can say it was a very busy day and the controllers had their hands full; although the controller losing site of an aircraft that had just departed his runway less than 30 seconds made the situation a little more dramatic than it needed to be.