Answer
Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
Your work as a controller in a taxi company is permissible and the salary earned from it is lawful.
Answering your question, The Fatwa Center at Islamweb, states:
Your work as a controller in a taxi company is permissible and the salary earned from it is lawful, as long as your work is to receive phone calls to book taxis, and monitor drivers to make sure that clients arrive at their destination on time, and so on.
The Islamic violations and prohibitions that may be committed by the customers and the ill-behavior of the drivers have nothing to do with the origin of the job (i.e., do not affect its permissibility), and the sin falls upon the one committing it.
Almighty Allah knows best.
Source: www.islamweb.net.