I had the same problem when I upgraded my phone, NanKate - non of the new ones seem to give an audible follow-up message alert. Had to settle for the flasher option (and they don't all do even that!) which is easy to miss.
On my old mobile, now defunct, I had a facility that if I missed a call it alerted me every so often with a quick ring. When I tried to get a more modern mobile I was told they don't ring now only flash a light, which is no good to me as I have my mobile in my pocket.
I use a PAYG phone not a contract one. Any suggestions please ?