How can I fix the handset on a BT Freestyle 1500 plus?

I have a BT Freestyle 1500 plus cordless phone. It all works apart from the red light does not light on the main base handset, and the caller cannot be heard on the same handset but they can hear me . All other features, and the extra handset and base work OK. The batteries seem to charge Ok and it has a new back-up battery. It is fairly old now, but we like the looks of it. Can you help please? Dennis Houghton.