Undisclosed Costs and Debit Order without consent

I received a notification from Tracker stating that my unit was not transmitting a signal. I contact them and they indicated that they need to send a tech out to check on it. The tech came out and indicated that they need to replace the tracking unit, due to a fault, and that there will be no cost as the unit is still on Warranty. Two weeks later, I get a message from Tracker, stating that and additional amount will be deducted. I contact them and they then told that it was for a Call Out fee for the Tech. NONE of this information was shared with me, in any of the discussions I had with them, meaning I did not acknowledge or agree to any of this, yet they choose to go ahead with an additional debit order without my consent.