Hello Ana,
I'm sorry to tell you that we are not the right adress to contact to get a job as a Hiwi. Wer are only a group of students who function as a kind of representatives for all students of English.
To get a job as Hiwi you usually have to be a student of either /both English linguistics or English literature.
But nonetheless, you should contact the following offices. These are the offices of the professors who might offer you a job.
leuchtenberg@anglistik1.rwth-aachen.de (English literature) Sekretariat@anglistik2.rwth-aachen.de (Historical English linguistics) roentgen-shoukry@anglistik3.rwth-aachen.de (Modern English linguistics)
Hope this helps. Good luck,
All the best, Britta Weber (Seniorat Anglistik, RWTH Aachen)