Pay back the money

Following my last complaint onHello Peter, Mix Telematics, rectified their error by swopping the incorrect device with correct one. Their telephonic response was extremely quick and the device swop was done within a few days however, although I have been correctly debited for the new month, my refund on the excess debited tge previous month had still not been done as per their promise. When I called their debtors department, I was told that she can see a request for a credit note and she will follow up. It has been 3 weeks since then and I still have not had any feedback. PAY BACK THE MONEY, MIXTELEMATICS!!!