Cancellation via website – FlixBus & FlixTrain Review

I am unable to cancel my booking on your website. You have no place to do this, so I tried “contact”, butThe drop down for “select your subject” does not work on my mobile device. I am TRYING to cancel booking number 8064517674 on 18 May, Avignon to CDG airport, Paris., name Sterling!!!!?
Review by sush2 on FlixBus & FlixTrain.