If someone with local knowledge posts a reply, please give their answer priority over mine. I don't live in your area and I have no personal knowledge of local taxi services.
However, I used to work for the railways and I know that any company which makes it onto the 'TrainTaxi' list can normally be regarded as reliable. (These tend to be the larger firms, who have the flexibility to cope when, say, a driver phones in sick).
I've just checked the National Rail website and the relevant companies in your area are as follows:
ABM 01384 838383
Falcon 01384 393939
Dudley Taxis 01384 230010
5 Star 01384 255555
Chris