Dear Bhavi ji,
OT is a part of earning and PT is payable on gross earnings during the calendar month. When you make payment to employees more than one occasion in a month, all such payments should be clubbed together to ascertain the PT monthly liability on total gross earnings in a month.
You are making payments twice in month. You need to adopt some system by which PT is to be deducted from total gross earnings during the month.
I suggest that you should add the amount of OT paid in previous month in the current months' gross for the purpose of PT deduction. This, I feel, is easy way.
Alternatively, you have to ensure the deduction of difference in PT due to OT payment from the payment of OT.
Hope you understand what I said.