20. Charge and set- off in respect of shares or interest of member. A registered society shall have a charge upon the share or interest in the capital and on the deposits of a member or past member and upon any dividend, bonus or profits payable to a member or past member in respect of any debt due from such member or past member to the society, and may set off any sum credited or payable to a member or past member in or towards payment of any such debt.