I have had my demo system for some time and it worked perfectly originally. However after installation of a Sonos system and Sky Q I have had nothing but trouble and decided, at least as a temporary measure, to disconnect my Deco system.  I have removed all the Deco units and while this leaves me with a weaker WiFi from the  Sky Broadband router, the Sonos and Sky Q including mini boxes are much more stable. 

Despite removing all the units I am left with the Network the deco created still showing. I can connect to it with the same password and there is some (very limited) internet connection. I also find that on a couple of occasions I have lost the Sky connection and have been unable to sign in but can still sign in to the deco system. This is corrected by resetting the router. 
 

I am not technically minded and I do not understand why I still have this connection available when the hardware has been removed. Should I have done something else before removing the deco unit? I did try to research how to do it but could find no guidance. What can I do now?