This is the correct format /etc/network/interfaces for wifi
source /etc/network/interfaces.d/*
# Network is managed by Network manager
auto lo
iface lo inet loopback
iface wlan0
hwaddress ether xx:xx:xx:FC:76:3F
Are you using Wired connection Ethernet (eth0) or WiFi (wlan0)?
Try this:
sudo nmtui
Go to "Edit a connection"
Choose "Ethernet" OR "Wi-Fi", whichever you are using, then highlight "Edit" and press Enter Key.
You will see MAC address under "Device"
.