Firstly, you should make sure that do you have maken a backup before.
You can find the backup of contacts in the following place:
1. google account, if you have a google account and open the sync, the account might make a backup for your phone before, thus,when you lost your contacts, you can recover them from google account.
2.Official PC companion in computer, generally, you should upgrade the android phone via official PC companion provided by manufacturer, and this PC companion will make a backup for the phone when you connect the phone to the computer,and lauch the application,if you have open the automatical backup fuction.
3.3rd-party android phone assistant, I think you might have installed a 3rd-party android phone assistant for installing apps conveniently, and most of android phone assistant have a backup feature as PC companion.
so, you should try the ways above to recover contacts.
However, if you do not have any backup, and you have a vcf files in the phone'SD card, I think you can recover the vcf files from the SD card. learn more here:
Android Data Recovery
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