BT Converse 325 corded phone - LCD display not working - how can I fix it?

The LCD display screen on my BT Converse 325 corded phone is completely dead, despite my having replaced the 3 AAA batteries that it runs off with new ones a couple of times (in case it was the batteries that were faulty), carefully ensuring the correct battery polarity, etc each time. BT is no longer offering support on this make and model of phone, so if anyone has any idea what I could possibly do next to fix it, I would very much appreciate it! Many thanks.