What is the ruling on using a purchase voucher provided by the bank as a reward, knowing that the account is current and non-usurious?

The balance in a current account is considered a loan to the bank, and any rewards the bank grants on this loan are considered usury (riba). Dr. Muhammad ibn Saud Al-Osaimi has issued a fatwa stating that these points are "the forbidden usury on a loan, which is the usury of Jahiliyyah (pre-Islamic ignorance)." Therefore, it is not permissible to benefit from the voucher obtained from these points; rather, it must be given to the poor and needy, and one must completely cease dealing with usurious banks.