Outside beam set off by sun

ADT installed 3 outside beams at my premises in April 2015. The back beam was working fine till around September 2015 when it started setting the alarm off 'for no reason', only during the day. I called ADT in November 2015 and they sent a technician out that said it is the glare of the sun and that they would have to install a cover. They never got back to me and I called then they claimed that they never installed the beam. Eventually after I had to put up a huge fight they send the 2nd technician. He found a resistor not connected properly but he also suspected the sun recommending another type of beam. I phoned them again to follow up and they made an appointment to send someone again. On the morning of the appointment they phoned to say they can't actually work on the control panel because another company is now doing my alarm monitoring (I did cancel my contract with them in October). That is nonsense as the new company gave me an installer code that they can use to work on the panel. On 4 January I called again and asked to speak to the technical manager to try and resolve the issue but she was in a meeting and would call me back but that never happened.