Duplicate Contacts

This caused a problem yesterday when, in the car, I asked Siri to share my ETA with Mary. Siri responded with “Which Mary Hewson? Mary Hewson or Mary Hewson?” As you can imagine, answering “Mary Hewson” just provoked a repeat of the same response!
I had a quick search and found a page which dealt with duplicates on the Mac only but said that if contacts were duplicated on iCloud.com, I should contact Apple Support, so I thought I’d start here!