Porsche maintenance

I have a 2008 porsche boxster 2.7L and recently took it in for new front brake pads - they had worn down, but not to the point where the sensors attached to the pads had been triggered to send a message to the car display. I thought that because the sensors hadn't been triggered they wouldn't need replacing. However, the garage replaced the sensors as well as the brake pads (at a significant extra cost and without informing me). I am basically worried that I have been ripped off. I would be really grateful for your advice on this one. As a young English woman living on my own in Dubai I don't have anyone I can ask for advice. Thanks! - Kate