6. Subject to the provisions of the last preceding section, an instrument so framed as to come within two or more of the descriptions in Schedule I ¹[***] shall, where the duties chargeable thereunder are different, be chargeable only with the highest of such duties: Provided that nothing in this Act contained shall render chargeable with duty exceeding three Taka a counterpart or duplicate of any instrument chargeable with duty and in respect of which the proper duty has been paid ²[* * *].