How can a deceased father's debt to a telecommunications company be paid, given that the indebted phone number is unavailable and the company refuses to search by name?

The debt of the deceased must be paid, and their accountability remains encumbered until what they owe is settled. The Prophet, peace and blessings be upon him, said that the deceased is held by their debt until it is paid on their behalf. If you cannot reach the creditor, contact the company that contacted you and inquire about how to pay, or search for the debt under the deceased's name. If you are unable to find a way to pay the debt and the company refuses to accept it from you, you may give the amount in charity on their behalf. It is inconceivable that there would be no way to settle the right or that the company would refuse to accept the amount.