Is it permissible to subscribe to an unlimited internet service through a usurious bank, knowing that the service provider only offers this service through the bank, and that subscribing through other companies is more expensive?

It is not permissible to open an account in a usurious bank, even with the intention of disposing of its interest, because it constitutes entering into a forbidden usurious contract. The account must be closed and dealings with the usurious bank severed immediately, along with repentance and disposal of the usurious interest. Paying the monthly internet subscription through a usurious bank is permissible, with priority given to a permissible alternative. However, it is not permissible for one's salary to be deposited in the bank or for funds other than the subscription amount to be placed with it for use in its forbidden transactions.