During the final approach, I deactivated the autopilot. The alarm started ringing. Instead of going off by itself after a few seconds, the alarm kept ringing until after landing. Even the master caution button did not help to deactivate the alarm.

Same here. 

Plus one. Had to cut out sound volume for aurals in EFB

I had this issue too 😞

I had this issue as well but sound ended when switching to outside view and then back into cockpit.

Press the red button on your sidestick in the Cockpit 

That worked also for me, I have an AP disconnect button set on my joystick, pressed it and the sound was out.

same. came here just to find out if other players facing similar issue.

press red button on the sidesstick in the virtual cockpit 

 

The A300/A310 alarm can be a real ear-driller if you aren't used to it! Usually, you just need to hit the 'AP Off' button on the yoke a second time to silence the cavalry charge. If you’re clicking the dash buttons instead of using a mapped key on your joystick, it tends to just stay in that warning loop. I actually ended up using a simple site like https://onlinealarm.co/ on my second monitor to set 'reminder' alerts for my descent top-of-climb points, mostly because I kept getting distracted and missing my altitudes, which triggers even more annoying alarms in the cockpit.

Welcome to Airbus. 🙂 
As others have pointed out, the AP disconnect function requires a double press- 
Once to disconnect autopilot and another push to silence the warning alarm.