Is it unlawful to take a taxi fare from the company when using my personal transportation subscription to carry out work tasks?

You are not permitted to bill your company for taxi fares when, in reality, the situation is otherwise. Rather, you must inform your employer of the true state of affairs. If they accept, then there is no sin. If not, then it is not permissible, because it is deception and consuming wealth unjustly, which is forbidden by His (the Almighty’s) saying: "And do not consume your properties among yourselves wrongfully."