Sagemcom router port foward loss

[#1]

Hi can anyone help I have just joined plusnet and recieved the new sagemcom router which seems ok but today I had someone come and connect my dvr cameras to this router by using the port fowarding process, this was great and everything worked great but  when I tried to view this an hour later it was bringing up a message that the IP was inexcessable , the problem I have with this is I have a static IP address and this has remained constant . When I arrived home and went into router settings the port fowarding was lost and when I put the details in again it started to work again , it appears that if there is no activity for a period of time it just forgets about this setting rendering it useless so can anyone tell me how to remedy this
Please be easy with the replies as I'm not that technically minded
Thanks col

[#2]

I've not heard of that happening before.
Has it happened again?

[#3]

Hi this is continually happening and not allowing me to view the cameras , what I have discovered is that when I go back into the router settings and highlight the protocol and and change to both and save it works again for a short period and then I'm back to the same situation . I have also tried to change to a different port but I get no warning of changes that are happening not like when I enter port 80 and this only ever warns me on port 80
Could you please tell me how to resolve this or have I got to purchase my own router
If I do what info do I need to set it up
Thanks col

[#4]

Hi just say I've done a search of this router on the forums and it doesn't look like mine is an isolated case