1) what is the content of tape recorder? may not be strong evidence, don't worry too much
2) if i were u, i would stand still & not settle at lab dept, then put it to tribunal; but remind that tribunal would not consider much on your evidence of being paid or not however, it is better than nothing support; (their aim is settling only); keep stand still if u already paid, just pay what the maid should has, that is enough, don't be frightened by whatever the 'judge' says
3) physical assult is a criminal case, the suspected would need to give statement to the police, police & 律政署 will consider whether should put the case to court. if it is not true, just put down what's happened on "that date" on the statement + your story as mentioned here