It happened to me and my brother too (in separate occasions), with the official client.

The data and music "being played" with our accounts seemed so random and niche that I doubt that it was result of human interaction, seemed like something wrong with their DB. Also, changing the password didn't fix it.

Had to change the password and also delete all the data in the account, losing also my data of course. It had so much garbage that it was pretty much ruined anyway