Is working in the sales department for a company that provides software services and website development, in addition to services related to the stock market, permissible or forbidden?

It is not permissible to practice any work that involves aiding in a forbidden matter, based on the Almighty’s saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." This includes aiding usurious institutions, even if it is merely guiding them to services that assist them in carrying out their forbidden activities.

So, if the mentioned service aids these institutions in their forbidden activities, then it is not permissible for you to work in presenting it. You must strive to leave work in the said department and search for a permissible job, unless you cannot find what suffices your necessities. In that case, it is permissible for you to remain only to the extent of necessity, while diligently searching for a source of halal income.