It happened to be that a couple of years ago I happened to develop two of every email. I then told this app to get rid of the duplicate contact addresses, and what it did was to get rid of every single address. Supposedly it was supposed to back everything up to the icloud but I could never find it. I called Apple support and got a very nice woman at the first level of support who, after 30 minutes said she was going to get me to a higher level of support but somehow we lost each other. I then called support again and immediately said I needed a high level. The woman who answered looked up my account and immediately transferred me to high level who knew exactly what to do. Problem solved! However, outside of this program destroying my contacts list on my phone, there were other TERRIBLE characteristics that this app had. THERE WAS NO TELEPHONE NUMBER WHICH YOU COULD CALL and YOU COULDNT EVEN FIGURE OUT WHO THE DEVELOPER WAS using three search engines. Recently I had decided that I wouldn’t buy software from any company without a support telephone number. I sent an email TO SUPPORT ABOUT 6 or MORE HOURS AGO AND HAVEN’T heard a thing. BTW, I’ve had Mac computers for fifteen years, and in times past even programmed mainframes, so I think I am reasonably computer literate.
Sorry for the bad experience. If you delete the contact information by mistake, you can retrieve it in the contact backup. If you have not made a backup, the deleted contacts cannot be retrieved.