Hi,
Could you please try to use following code:
MediaFileInfo mediaInfo = MediaFileInfoProvider.GetMediaFileInfo(imageID);
MediaLibraryInfo libraryInfo = MediaLibraryInfoProvider.GetMediaLibraryInfo(mediaInfo.FileLibraryID);
String urlFile = MediaFileURLProvider.GetMediaFileUrl(mediaInfo, CMS.CMSHelper.CMSContext.CurrentSiteName, libraryInfo.LibraryFolder);
Best regards,
Michal Legen