Can't Remote Desktop through Plusnet Fiber Extra

[#1]

I recently had Plusnet Fiber Extra installed at home and have been racking my brains trying to get remote desktop to my office working. First things to say are:
1) Remote desktop to my office works fine in multiple other locations on other ISP's. I've tried it at clients and I even have it working when tethering from my phone sat at home. So it doesn't seem to be an issue with things at the office.
2) When connected to my Plusnet Fiber Extra broadband at home and trying to remote desktop to my office, I get the standard could not connect error. I have tried calling Plusnet and we tried having the Broadband firewall set to both the 'Off' and 'Low' setting. Both of which made no difference. We also set up port forwarding in the router and even disabled the router firewall for testing. But still no luck!

I've kind of run out of ideas of things to try. Any suggestions would be greatly appreciated, but it certainly feels like Plusnet are blocking something, as it works fine on the same laptop when I change over to my phone hotspot.

Thanks
Alex

[#2]

I have tried calling Plusnet and we tried having the Broadband firewall set to both the 'Off' and 'Low' setting. Both of which made no difference

Did you disconnect & reconnect after the firewall change ? It doesn't take effect until the PPPoE session is reconnected

[#3]

Yes, I was on the phone to Plusnet support at the time and we tried both the “off” and “low” setting, making sure to restart the router after each change.

[#4]

@alexpettitt When you upgraded to Fibre Extra chances are you will have been given a new IP address. So as you are trying to connect from your Home to your Office the Plusnet router at your home has nothing to do with it, all it will do is push your request out on to the wire. It is the Office denying the request.
 
What you could do is check your office configuration to see if it is blocking your IP because of the change.

[#5]

We use the Cisco VPN software for work and I have no problems connecting into work from my work's laptop from home.

A while back there were some VPN issues caused by some PN IP addresses not being seen as being in the UK.