A few things you can do: a) Ask HR what entity is paying you (probably still A) b) Ask your Boss which company s(he) is working for (reporting lines are importa

A few things you can do: a) Ask HR what entity is paying you (probably still A) b) Ask your Boss which company s(he) is working for (reporting lines are important in HR's eye's) c) Once you know what organization is paying you and what reporting lines you report into, then you can have a better idea of where you actually work. d) If it's all A and you are doing a whole bunch of work for B, then it's time to have a sit-down with boss to clarify things. e) You can always ask for a legal (sometimes free) consultation about what your rights are, what your tax implications are, etc...