We do what we have said = Chúng tôi làm những gì chúng tôi đã nói.
I still think "We do what we say" or literally "We do the things that we say" are the most accurate translations. To know if you have done a good job translating, use the translations and convert them to the original language. Convert these sentences into Vietnamse and you'll know what I mean.
We do what we say
We do the things that we say
We do what we have said