A doubt about neobux renting refs

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yesterday i rented some refs for first time and i enabled the autopay...... Today i saw a reduced renting balance and increased renting date!! i thought autopay will be enabled only if the after 31days of renting... now if i rent more and more and i keep autopay on when 20days are left for the first rented refs ....all the other refs will eat away my renting balance.... pls help me ....wht should i do?