You should reach out to the T-Force team on Facebook or Twitter. From my understanding, applying a $400 credit is beyond what the regular tier of CSR's can apply.
When you speak to representatives, do they give a reason for your credit not being issued? If all qualifications are met and you properly submitted, I am not sure why it wouldn't have been properly issued.
Have you reached out to T-Force like suggested above? We can give general info through here, however we don't have access ere on the support forums.