This problem has to do with the sound file that you are using. The sound file is missing android_loop metatag if it is only ringing once. If the ringtone doesn't loop in the preview on your phone then it is missing the tag. You can check for the tag on your computer by opening it with vlc player and go to tools->media information->metadata. Here's instructions to add the tag to whatever file you want I find on Google. I used it myself to get my ringtone to loop.
- Download and install Audacity (audacity.sourceforge.net)
- Open the ringtone file in Audacity, note you can use mp3/wav files as well, Audacity can convert them into OGG.
- Select Open Metadata Editor for the File Menu
- Add a new tag called ANDROID_LOOP and set the value to 'true'.
- Click OK
- Select Export from the File Menu and select the Save As Type format as Ogg Vorbis Files.
- Click OK through File Save and Metadata dialogue window.
- Copy the new ringtone file onto your phone.
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