Hi Thawatchai,
Greetings! My name is Neldy, your iTunes Store Advisor. Thank you for contacting iTunes Support. I can see that you were billed twice by iTunes for your recovering your missing ringtones. I know how concerned are you to rectify the said incorrect charge as soon as possible. I am happy to provide the information you need to reach a resolution.
After reviewing the circumstances of your case, we determined that issuing you a refund for your duplicate purchases of ringtones are an appropriate exception to the iTunes Store Terms and Conditions, which state that all sales are final. In seven to ten business days, a credit of 3.87 USD should be posted to the credit card that appears on the receipt for that purchase.
Please know that Ringtones can be downloaded once and it is not featured in your Purchase Page due to copy right and content providers permission for distribution. This is the reason why you cannot redownload this item back to obtain a copy again.
The instructions from the link "itunes.com/restore-tones” are applicable for iSO 8.1 and since we are already under version 8.4, the link may no longer be compatible for you.
It is always advise to back up your purchases especially Ringtones because from time to time, the iTunes Store updates the items in the catalog to ensure the highest possible quality for our customers. Once the item is already modified, there will be a tendency that you can no longer and I can no longer repost the item for you.
This article explains how to create and maintain an up-to-date backup of your iTunes library, which can be useful if you ever need to restore your purchases in the future:
iTunes: Back up your iTunes library by copying to an external hard drive
https://support.apple.com/en-us/HT201625
As always, my goal is to help you with your concern as quickly and accurately as possible. If you still have more questions, feel free to email me anytime and I will be more than happy to assist you.
Sincerely,
Neldy
iTunes store/ Mac Apps Store Customer Support