Your own evidence might consist of your phone logs at that time, either retrieved from your device or, more impressively, provided by your service provider. It all depends on how sure you are you were not on the phone. If, like me you NEVER use your phone in the car, you may feel sufficiently sure that you want to pursue this; after all, they might have mistaken the car or made some other sort of error. You can certainly start by examining the phone you had with you (I presume that is common ground) and look at your call logs at and around the time you were alleged to have committed the offence. Remember that calls can be made using data too, with WhatsApp for example, so you need to check those as well. Cut all the emotion out - it simply clouds your thinking. If you are getting more confident after checking your phone consider those next steps with your provider. If your logs aren't helpful you are probably best taking it on the chin, I suggest.