Horrible service from Mix telematics

in 2019 i changes cars, whereby i notified Beamie and they came to install the beamie device in m y new car, at that time i cancelled the Beamie device on the old car, however they continued debiting my account, an agent advised that they would cancel it, which never happened, i since reversed the amounts debited incorrectly, of late they have been sending me sms's threatening the day lights out of me for a R117.00 that's rightfully mine, i would send email with proof and to date they have not responded, yesterday i received an SMS notifying me that they have handed me over to attorneys, when i called Mix telematics they told me that they have no proof that i cancelled May 2019 when the new device was placed in my new car. they can only see the cancelation was logged in Nov 2019, after i advised them that i was guided by a consultant telephonically while arranging for the new device to be installed.