Hi,
If your quota request has been declined then your next steps will be to inform your dedicated sales representatives (if you have any). If you don’t have any dedicated sales representative, then please contact the sales team [1] for further assistance. Furthermore I would recommend you to write an email to this email address gc-...@google.com and inform them about your concern. I hope this helps you to resolve GPU quota issues.
[1] https://cloud.google.com/contact/