Hello and welcome to JustAnswer. Please note: This is general information for educational purposes only and is not legal advice. No specific course of action is proposed herein, and no attorney-client relationship or privilege is formed by speaking to an expert on this site. By continuing, you confirm that you understand and agree to these terms.
I am sorry to hear about this situation.
Is it going to help to send them a letter stating their need to pay outlining they took the files and I have both receipt of them taking the files and that I have records of them hitting the development site until I sent the invoices.
Likely, yes. This is what is known as a demand letter, which basically states "pay me or I sue you." While this is not mandatory, it is often used and to a good degree of success, against individuals and businesses. Attorneys sent them out all the time. The demand letter offers a way to settle the matter without having to resort to litigation, which is both expensive and time consuming.
It would help to use counsel if possible. If one decides to send the letter without using counsel, it would be helpful to use some verbiage to show that the threat is serious, such as breach of contract under New Hampshire: "An action in contract is based upon a failure to perform a special agreement and the damages recoverable are the difference between the values of the condition promised and the actual condition, including incidental consequences fairly subject to contemplation by the parties when the contract was made." Lakeman v. La France, 156 A.2d 123, 127 (N.H. 1959).
A demand letter normally gives about 10 business days to two weeks to make payment.
I hope this helps and clarifies. Please use the SEND or REPLY button to keep chatting, or please RATE when finished. You may always ask follow ups at no charge after rating. Kindly rate my answer as one of TOP THREE FACES/STARS and then SUBMIT, as this is how experts get credit for our time. Rating my answer the bottom two faces/stars (or failing to submit the rating) does not give me credit and reflects poorly on me, even if my answer is correct. I work very hard to formulate an informative and honest answer for you; please reciprocate my good faith with a positive rating.