Firstly, don't address the recipient ever as "Dear sirs" There is a good chance that the person reading the letter may be female, and an even better chance that not all men work at that place of business.
please release the payment enclosed
This kind of sounds like you enclosed, provided a payment with the letter.
This letter is to introduce Mr/miss Jones
You don't know the gender of the person that will be receiving/handling your money? Do you at least know the person's first name? This would come off as possible spam, scam, but at the very least awkward. Just say the person's full name, let's pretend it's John!
please release the payment enclosed you may find the terms of reference and the action plan
So they have to submit the payment before they can find the terms of reference and action plan? Or is the terms of reference and action plan included in the letter/envelope already? It's unclear what you're saying here. I'll just go with you have that included until you say otherwise.
So I'd write it formally like this:
This letter is to introduce you to John Jones who works as the translator in our project. He has accomplished the following codes of the action plan, which is attached to this letter for reference along with the terms of reference. Please submit payment for the bill enclosed.