All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If by the expression the bill must be ‘warranted by a bank’ you mean that the bank is bound to pay the debt to the seller when it is due whether or not the customer had paid its value beforehand, then this transaction is a warranty and in principle it is permissible. However, according to the view of the majority of the scholars it is not permissible to take a commission on the warranty but it is permissible for the bank to take a fixed fee for its expenses and this did not happen in the above example.
However, if the bank pays on your behalf the installment when it is due and then it takes the amount from you more than what was paid, then this is clear Riba (interest and or usury), because in this case, the bank gave a loan to the client with an interest.
Allaah Knows best.