I have a 2011 Peugeot bipper van, it’s ex Royal Mail, the 12v socket doesn’t work, I checked the fuse under the stearin wheel and it’s ok?

Some cars have a short wire built into the socket that is a fusible link. Take the socket out and check for power to the socket middle contact on each side of the fusible link. If the fusible link is fried I've replaced them with a piece of regular 12 volt 14 gauge wire to get it working.

I don't know about a Bipper but on my Peugeot van the socket originally only worked when the ignition was on to prevent battery discharge if something is left plugged in when the engine was switched off. Check your owners manual to see if this is is the case with a Bipper. If not you will need to check if there is voltage and earth / ground to the back of the socket, with a volt meter or test lamp, and if there is the socket is probably faulty. If not you will need to check the wiring back to the supply.

On my van I rewired the socket, via a 15 Amp inline fuse, to a permanently live supply to overcome this.

I have tried a few different appliance it nothing works, I took the socket out and noticed another clip that plugs into it, I tired to plug the new connector into the socket and that one didn’t work either

Test the socket itself with a multimeter. If it is getting power then the problem is with the contacts in the socket making a connection with whatever you are trying to plug in. If it isn't getting power, then you need to look upstream of the fuse for the problem by tracing the wire to the power source and checking continuity.

You'll need to follow the wire to make sure it is connected properly with no breaks in the wire.