Your mother and you need to contact your cousin about the bill and find out if the cousin made the calls. One way to confirm is to call the number in Nigeria and ask the person picking up the phone if he or she knows your cousin.If your cousin made the calls, your cousin needs to pay the bill. If the cousin refuses to pay the bill, a legal action needs to be filed to get the money to reimburse your mother for the payment to be made.You should call the telephone company as well about the charges to put it on notice about unauthorized use of your mother's telephone. Perhaps the telephone company may have a policy of reducing the bill in such a situation.Good luck.