Telkom voids my warranty for no good reason

I have a cellphone contract (Samsung J7 Pro) at Telkom. In December I accidentally updated the software (I didnt want to, but the notification kept popping up over the whole screen and I accidentally clicked update). This update caused the touch screen to stop working (a common issue apparently with the android 8.0 update and the J7 Pro after looking it up on the web). I took my phone to Telkom to be sent in and repaired. They have now for some reason deemed the warranty void (the phone is only 10 months old?) and have quoted me over R4000 for the repairs.