***** or theft?

On 21 May 2014 Chubb serviced the alarm at my house. The payment for this, R960.97, was to be deducted by debit order. On 31 May 2014 Chubb deducted R1921.94 by debit order. When I queried this amount, they could at first not explain it. They phoned me back later that day and said that it was a mistake on their side and that it was twice the amount that should have been deducted (R960.97 x 2 = R1921.94). According to them some of their debit orders went through double that day and they had to stop their system. They paid me back R960.97 on 9 June 2014. Which meant that they have been paid R960.97 since they paid back only half of the R1921.94 that they have deducted. During April 2015 I received an invoice dated 1 April 2015 for R960.97. I phoned Chubb Bloemfontein and spoke to Lynette who assured me that it was a mistake on their side and that it would be rectified. I went to Chubb's offices with a copy of my bank statement to proof the transactions that had taken place a year before. Lynette assured me that they were aware of the problem and that it would be rectified. Chubb kept sending me invoices. On 21 September 2015 Chubb deducted R960.97 by debit order. Is this *****?