You do realise when you port forward you have to create the rule and then apply the rule to the device , sometimes restarting the devices helps, and assign to Mac address and so on
So basically it's out of contract has engineer reset , either you will find a way to fix it, or call an engineer or have a new alarm installed
It's still a case of weighing up cost of what your protecting against what it costs to fix alarm
Never had a problem bashing them in lofts and cupboards , so assume you walk away if they insist .....
Only issue I see with loft is as a house basher , the house Lasher's lash the stuff in and customer never goes up to see the mess
Just to add to the public search although not completely your case but
Upgrade upgrade upgrade , even those paying monthly contracts paying far to much to maintain rubbish (not everything but most is rubbish) and it's not the installer / maintainers fault no one wants to pay.....
Technology has moved on
Your hardcore
So hiwatch is the DIY market for hik
But will debenhams give you any after sales support , pay a little more and buy from a security dealer
Compatibility is normally done via onvif , if all IP stuff, if it's all analogue then hik uses tvi I think and some of there cheaper stuff might have switchable outputs going from normal video to and and tvi and so on
But if you renovating good time to scrap what you have , as above replace DVR to hybrid type which accepts some analogue and ip