Same thing happened my BF when he was working in Rome Hotel in Pattaya
At the end of first month they told him he wasn't being paid his agreed salary as he had been in "training" so we wrote if off down to experience
In the second month he racked up 40 hours overtime (they were short staffed in reception) and they refused to pay any of that (despite promising to) and only gave him half his salary.... as he was once again "training" - no idea how you can be in training when you are the only one in reception!
He quit at the end of month 2... Thankfully the business failed not so long after and the owners got everything they deserved!