Is sending money via phone (Flexy), where an additional amount is deducted from the balance as a service fee (10 Algerian Dinars), considered usury (riba)? And is it considered usury for the seller to take an additional amount for himself (10 Dinars) in addition to the company's fees?

Transferring call credit from one mobile phone to another does not fall under usurious sales, as it is a sale of benefits, not money. It is permissible to pay the fee charged by the company for the transfer service. As for the seller taking an amount for the transfer, if he is contracted with the company, he is not allowed to take anything from the credit owner. However, if he is not contracted, he may take an agreed-upon wage for his work.