BOUGHT RECHARGE VOUCHER FOR MY LANDLINE PHONE BUT "THE VOUCHER HAS BEEN USED!

My mom is a pensioner! And she bought a R30.00 voucher for her Telkom Landline for her to make the necessary calls. The pin number: 1 ********** 9 ********** at Pick a Pay on 31/08/2017 at 09:56 am with serial number: ********** ********** 1010. BUT the voucher has already been used!! Not by her obviously! After several phone calls NOBODY can help her! It is pathetic!!! It is only R30.00 but that is money that she cant through into the water! Could somebody please assist me!! Or tell me WHO to contact!! I wonder how many people experiences this problem!!!