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I'm sorry to hear that.
I suggest that you raise this with your local support team to proceed with this in the best possible way.
Local support.
At the service center they perform pressure tests to see if there's something wrong with the phone which makes the phone take in water somewhere else. If it passes this test the caps cannot have been closed properly when the phone was submerged in water, as it would not take in water if they were.
I'm not really sure what you mean but if the service center has ruled out the phone there is unfortunately not much to do. They might be able to repair it for you but it won't be covered by warranty. Contact your local Xperia support for more information.
And please do not write 3-4 messages in a row, try to stick to one as it's much easier for me and anyone else who is trying to follow the thread.