Veneers turned yellow. Is there anything I can do to whiten them? (Photo)

I paid 15,000 to get veneers and 5 years later they now are dull yellow. Not All of them. I am reading and it is saying that veneers do not turn colors so I do not understand how this happened. I do not have the money to get them replaced as I paid 400 monthly and just recently paid that off. I am so upset and distraught and feel like a wasted all this money. Is there anything I can do to whiten without having to replace these veneers.