How to change mac-address or tricky dd-wrt protection?

Question

Network administration

Hello.
I faced such a problem:
There is a router with dd-wrt firmware that distributes wifi, ip is distributed automatically.
I connect to it from a laptop under kali linux and everything works fine.
Now I want to change my wifi card mac address:
ifconfig wlan0 down
macchanger -r wlan0
ifconfig wlan0 up
The ifconfig wlan0 command says everything is ok - mac is different.
I connect to the router, the mac-address becomes real again (i.e. native) and ip is again the same as when I first connected.
I tried to delete the connection, the mac-address is still set to the real one.
What am I doing wrong? Or is it some kind of clever dd-wrt protection?