Lancet refuses to refund my mother

My mother has been a well paying customer to Lancet Laboratories but they refuse to refund the money she mistakenly sent to their account.This is the second time it happens and she didn't remove the account from her banking app because they still had to refund her for the first payment. The account number would serve as proof that she indeed transfered funds to their account. So she hasn't been refunded for both of the payments. They do acknowledge the payments made and she also asked our bank to assist in reversing the second transaction back to her account but Lancet refuses to give her the money. For the first payment the consultants said she should send them proof of payment and she did, but she still didn't receive her money. She called again last week and the consultant said she will send her an email of all the documents they require about the payment and she still haven't received it today. She tried being patient but her patience is running thin, she wants her money back as soon as possible. Lancet Laboratories please give my mother her money back.