RDC Stopped Working and Remote Access to Work CCTV is Intermittent

I have a small office network that has Sonicwall TZ210, a TP-Link router (TL-WDR4900) and a Server running Windows 2008 Server.

There's also a CCTV system that I can access from home.

I also have a dyndns.org account.

3 months ago, everything was working perfectly. Then we had a new telephone system installed and configured - The office network still works, we can connect to the server, access files and access the internet but something that the engineers have done has now resulted in the problems in my subject line:

1) Remote Desktop Connection no longer works at all.
2) I can only get access to my CCTV intermittently via mycompanyname.dyndns.org:9009 - I can't work out why it works one minute and then later that afternoon it won't connect.

The following points may be red herrings and have nothing to do with the problem but I'm mentioning them for completeness:

• When it worked perfectly we were on a Cisco router. The engineers configured the TP-Link themselves.

• The engineer spent a lot of time tinkering about in Sonicwall so a setting or two might be messed up in there

• They entered the IP address of the telephone provider into the server. I think they had to do that in order to make the call logging feature of the new telephone system work.

Things I've checked:

• That my name is authorised to use RDC in the server

• That TP Link has got port forwarding for 3389 (RDC), 9009 and 50100 (CCTV)

• That my dyndns.org is assigned in the TP Link

I don't know what to do now or what else to check. Can anyone help?