Regarding the Monitoring, it appears strange that they left it for 6 months without Invoicing you. (am I correct with this). Do you realy need the monitoring - depends on the level of risk, the contents of your property and stuff like that. I have a fair idea which alarm compay you are with and they did teh same to me. If i picked up your situation correct it is their problem for invoicing you late.
In all these type of instances, as things get a bit tight, you should be able to negotiate with them.