Is it permissible to pay for a purchase with a Visa card over 12 months with a 1% increase on the amount, if the 6-month interest-free option presents a financial difficulty?

You have become indebted to the bank for the price of the mobile phone. If the bank agrees that you repay this debt in known installments, then this is permissible, provided you repay the price without any increase. However, if the bank stipulates an increase on the price for the delay, whether it is 1% or more or less, then this is impermissible, because it is explicit, prohibited usury (riba), which is one of the grave sins and one of the seven destructive sins.

Therefore, payment in installments over six months without an increase is the only permissible option. As for payment in installments over one year with an increase, this is prohibited usury, and it is not permissible for you to proceed with it.