Trade is often dearer than retail
I need a new laptop, if I have a company name on the order they want 1% surcharge for using a credit card
No co. name & no surcharge as I'm a consumer....
I've big one which was on the desk with pens in it.
There not much pormo stuff in the alarm trade.
Mugs, powersonic, duahu, dualcom... & an Eaton l keyring.
ADSL on the alarm telephone line will interfere with the Alarms ability to here the tones which make it stop dialing.
A "working telephone line" can have a ground fault can interfere with the Alarms ability to here the tones which make it stop dialing.
Normaly your contract would state the call charges are your responsibility.
There is probably a ground fault, star services or adsl on the line which interferes with the digi hearing the acknowledgment of the signal & to stop trying.
I'd assume the installer gets a report of sites which have't done a signal in 24hrs or report of sites with excessive signals.
You may ask them why they didn't act on the information... In turn they might ask why you run it up to £600.
I'd assume the goodwill of you telecoms provider & alarm co. would cover most of your costs