Is it forbidden to top up the balance through the station that charges a commission of 7 rubles for every 100 rubles?

There is no harm in topping up a phone balance for more than its cost, because the balance represents call minutes or service units (calls and internet), not money. Therefore, parity and immediate exchange are not conditions for it. This applies whether the selling entity is a telecommunications company selling a permissible service for an inflated price, or a bank/brokerage firm that buys the service then sells it for profit. The "Fatwas of the Permanent Committee" confirmed the permissibility of buying and selling phone cards at a price higher than their nominal value, on the basis that they involve the sale of a permissible benefit.