Welcome to the forum. To be able to reactivate the text to voice service you will need to ring the automated number 08005875253.
Give it a go and if you are still having problems, please comeback to me.
The way BT Text works the platform is sending the message as Text as there is a piece of equipment on the line that is giving the acknowledgement chirp. If there were no Text enabled phones on the line the platform would not recieve the chirp and would automatically send the message as speech. Would advise you to recheck your equipment. Other than that what network are the messages origtinating from. Is it TMobile or Virgin? These work somewhat diffrently.