1. About deduction, note the word "immediately preceding three months.." in Section 24 of the Employment Act as quoted below :
"... (2) It shall be lawful for an employer to make the following deductions:
(a)deductions to the extent of any overpayment of wages made during the immediately preceding three months from the month in which deductions are to be made, by the employer to the employee by the employer¡¦s mistake; "
2. Better get your commission first before resignation.
You can complain to the Labour Department about that deduction.