Burglar Alarm signal on Hub 5

We have had the same home alarm for 3 years. It can connect to the internet so we can set and unset it remotely. We agreed an annual fee on installation to keep this option going and it has worked fine. The montoring system is run by Pyronix.

Recently, the installer that we bought it from sold out to another company, so we went to Pyronix who were able to link us directly to them and the switch over went perfectly for about a week. Then, 2 days age, when we tried to set the alarm remotely we got a signal saying that the Security system is not connected to the cloud, please check your internet connection. The internet connection is fine throughout the house for all devices.

Pyronx, who have been as helpful as they can be, say there can be problems with virgin routers and we might have to change the hub settings to allow 2.4 and 5GHz settings. But I still can't understand why the same system linked with no proble up until 2 days ago.

I have the instructions on how to do this but have seen other posts where people have tried doing this and had problems with the signal throught the house. I have tried resetting the wi-fi link in the alarm key pad and tried switching the router on and off. 

So is resetting the router th only option?

Thanks