But I now can’t get into the D link with either its old IP address or the new one and if ipconfig it shows both addresses as default gateway.
The D Link should be given an address of 192.168.1. XX where XX is between 1 and 62. It should also be given a default gateway address of 192.168.1.254.
Your devices should only see a default gateway of 192.168.1.254, what addresses are you seeing?
You shouldn't be seeing the address of the D Link at all, certainly not 10.1.1.1, it is now just another device on your LAN acting as a switch and wireless access point rather than a router.
Are you sure you have changed its address correctly?
Well I thought I did but I can’t get back into it to make any further changes even after resetting to default settings.
Factory reset the D Link and connect your device to it via an Ethernet cable to make the changes. Make sure you save any changes. Once you have changed the settings on the D Link, make sure your device is getting an address in the 192.168.1.xx range with a gateway of 192.168.1.254. You should then be able to access the D Link with its new address you gave it.
Remember that your device will be getting its dhcp info from the D Link initially and then from the hub once the changes are made.