................die when it is called by a withheld number?
It's a BT Edge which works fine. But totally dies when those numbers call me. What's going on??!!!

"Die" ? Do you mean it turns itself off. Or does it crash, or not ring.
I think the best thing to do would be to call the help-line number in the manual and describe exactly what happens when a number with-held calls.

Turns itself off. Comes to life when put back in its cradle

have you got the service where it doesnt allow callers who withold their number to call?