Billed for SMS sent from Date Account to UK

Got a Data contract from Telkom with a Multi Sim. the Milti Sim was put into a Mobile Modem that i use for date only. I the get a account from Telkom for R508-50 for 333 SMS's sent on the morning of 4 August 2017 from 1;07AM to 1.30AM in this time 333 SMS sent to 333 different numbers in the UK. I then locked a dispute with Telkom Ref no ********** 5 telling me as it was sent from the multi sim i am liable for it. i will not pay for something that i did not use. How is it even possible to send SMS from a mobile modem. this is *******ion and ***** that could have only been done by somebody at Telkom that had the sim details. i was afraid to sign contract with Telkom now i know why they are unreliable and i will cancel my contract as soon as i can.