Hi
I would keep at it with the cage but make it a nice place to be
Do not just put him in there when you go out otherwise he will start to hate it

Start by making it a nice cosy place and feeding him in there with the door open
Keep the door open all the time so if he wishes to explore he can do

Gradually shut the door for 5 mins keeping him in the same room as you until you can extend the time
It will not work over night but neither will giving him an outdoor kennel when he is not used to it
good luck

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All the best
Pammy