The packet you’re sending is a Zigbee transmit request packet, so it’s not surprising that the 802.15.4 firmware doesn’t recognize it and hence doesn’t respond. Assuming the relay is connected to one of the I/O lines, packet type 0x17 (remote AT command) would be more appropriate.
Make sure you’re reading the right manual: the firmware types are different and you need the 802.15.4 product manual.
Also, it would be wise to upgrade from 10CD to the latest firmware. That may not help the immediate problem, but it will make life easier later.