Pay back the money

My wife bought 3 key holders from them she paid and they delivered, one of the Key holder was not in good condition it was of poor quality but my wife did not make a fuss about that because she said it will be expensive to return it back she will use a glue . Few weeks later she paid money into their account by mistake a sum of R3000 which the lady by the name of Anna Laser acknowledged that she received that money and she was going to pay it back it's been a month now she keeps on promising to pay back. Now she does not want to pay how to handle this.