Have you submitted a request to re-add it? If so, post the Submission ID Reference Number and staff can check on the status.
If not, you can submit to add it and, if you can get it, upload a screen capture of your name appearing in the on screen credits. This is what will prove it should be added and they should, then, not be able to remove it.
As to getting paid, IMDb just documents on screen credits. There should be no reason pay should be issues or withheld based on a listing on IMDb. That's between you and your employer and an IMDb page shouldn't have anything to do with it.
To submit the credits, go to the page for the film, click "edit page" and access the forms there to add the data. You can upload pics here then add a link in your submission, to this thread so they can view your screen shots of the credits (use the little camera icon at the bottom of the reply field here to upload an image).
See the FAQ page for
How do I add myself/my credits to IMDb?If you have a submission ID number already, you can get it from the emailed receipt you received or in your Account Settings page under "View your
submissions."
Post back for any clarification.
Best of luck!