Given the amount of money involved, the potential damage to your career, and the possibility that you will have deadlines related to tax returns/payments coming up after which you might not be able to fix some of this, I would suggest you do the following, concurrently:
1. Find an accountant.
2. Find a lawyer.
3. Keep written notes of everything, including copies of any relevant electronic communications and details of anything significant that was said to you verbally or on a call, by whom, and when.
4. Possibly start recording any future calls, but check the legality of doing so in your jurisdiction and any notice requirements first. (Don't ask the Internet, ask your lawyer.)
5. Don't talk to anyone at work about what you're doing until you've received proper professional advice.
Make sure the accountant and lawyer are yours, not the company's. Their advisors will have a conflict of interest and can't/shouldn't advise you personally as well. In any case, there is a possibility that the company lawyers and/or accountants have committed serious breaches of professional ethics and/or crimes here.
Make sure all your records are completely under your control, so if they kick you out of their electronic systems and the building at a moment's notice you still have all your evidence.
And from a practical point of view, don't assume malice or that this will end badly, because it may well just have been a naive but innocent screw-up, but do assume that whatever happens you might need another job by the end of this process and plan accordingly just in case.
And obviously don't post any more details publicly.
1. Find an accountant.
2. Find a lawyer.
3. Keep written notes of everything, including copies of any relevant electronic communications and details of anything significant that was said to you verbally or on a call, by whom, and when.
4. Possibly start recording any future calls, but check the legality of doing so in your jurisdiction and any notice requirements first. (Don't ask the Internet, ask your lawyer.)
5. Don't talk to anyone at work about what you're doing until you've received proper professional advice.
Make sure the accountant and lawyer are yours, not the company's. Their advisors will have a conflict of interest and can't/shouldn't advise you personally as well. In any case, there is a possibility that the company lawyers and/or accountants have committed serious breaches of professional ethics and/or crimes here.
Make sure all your records are completely under your control, so if they kick you out of their electronic systems and the building at a moment's notice you still have all your evidence.
And from a practical point of view, don't assume malice or that this will end badly, because it may well just have been a naive but innocent screw-up, but do assume that whatever happens you might need another job by the end of this process and plan accordingly just in case.
And obviously don't post any more details publicly.