I have shared the details with our team for further checking. Sorry, the site credentials were cleared when moving the ticket to a chat. So please share it again.
As I mentioned in the chat, it is unlikely that strings were translated by mistake because they need to be manually selected and sent for translation.
It is possible that the strings were automatically translated by default, but you can undo this if needed. Our team checked the translation jobs in the Automatic Translation Server and could not find any case where this happened.
Therefore please let us know the exact steps you have followed for 'mistakenly' to translate those strings. This information is must required to process a refund.
I opened strings from the menu, opened display all strings and instead of delete, clicked on translate. There no confirmation and due to the number of strings, the page timed out after like 30 seconds. I could not stop and then I found it used almost 10k credit. I could not find what strings were translated neither.
Currently I have 15k strings again, but did not touch it any more.
