My next move would be to phone RUKCC and ask to speak to a manager. Explain the problem to him and say you are not satisfied with your dealer's response.
I think you are within your rights to expect things to work and the
warning light is another, yet more serious, issue.
Bear in mind that Bluetooth is subject to interruptions and interference as most radio signals are. If you connect it once and set it up to maintain a continuous connection you will have less problems than if it has to search for available connections each time you enter the car and switch it on. The user-friendliness and reliability is probably more software dependent. Mine doesn't have Bluetooth but I use this on my pc to pc connections and there is no difference there; they can be erratic.
If you have started using an external aerial, I don't understand why you are having problems though? Maybe someone else can guide you through this as I wouldn't call myself an ardent mobilephone user.
It may be that many members will be away from their rigs this weekend so you may not have many replies until they return. I'm quite new myself here, but there are a good bunch of people who really try to help others. Altruism seems to reign supreme. I look forward to hearing what they say and what RUKCC do about your problem, especially the
p.s. You may also find relevant questions answered on Parker's forum pages. I hope the link below helps.