ADT Refusal to refund for services not delivered

I signed up with ADT in October 2015 and also requested the installation of 3 sensor beams. I was told by the installers that they will be unable to install the sensor beams and I requested them to cancel the installation. The cost of the installation was deducted from my bank account on 27 November 2015. Since then I have been calling ADT various times and each time I have been promised a refund by the next Friday. 3 months have passed and still no refund. It seems that they have a problem with refunds but conveniently no problem with deducting my subscription fees every month. I have no choice but to resort to Hello Peter since calling customer care seems to be useless.