What is the ruling on money earned from providing poor-quality website development services that quickly break down, and how can one absolve themselves of responsibility towards non-Muslim clients who have left the website or blocked communication, and who can no longer be reached to refund their money?

If you are certain that you owe someone a right due to deception and fraud, and there is no way to contact them, you can give charity on their behalf with the amount that clears your conscience. This is sufficient for absolution, due to the impossibility of reaching them. Ibn Taymiyyah stated that whoever possesses usurped items, borrowed goods, deposits, or pledges, and has despaired of knowing their owners, should give them in charity on their behalf.