This read pertains to activation lock; all iDevice possibilities are covered below. Note that no one here is authorized to provide instructions for removing activation lock and that activation lock is a theft deterrent system.
See Turn off Activation Lock https://support.apple.com/en-us/HT201441See this heading If you erased your own device. It says: "If you don't sign out of iCloud before you put your device in recovery mode and restore, it might remain in Activation Lock. That means you need to enter the same Apple ID and password that … was used when … [the device was last set up]."
[Use] forgot your Apple ID or your Apple ID password [to recover the needed credentials if you don't know them.]
If you have iOS 11 or later and your account is protected with two-factor authentication, you can turn off Activation Lock with your device Passcode. Tap Unlock with Passcode, then tap Use Device Passcode."
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Note that no one but the person that last set up the device will be successful in following the above instructions. So, if you are not that person, you will need to get the required password from the person that last set it up (i.e., the guy that erased it). Can you get it from him at the repair shop?
If you are the last person that set it up and can't follow the instructions successfully, then you will need to contact Apple Support and present your original purchase receipt for a pertinent device from an authorized Apple seller with the device’s serial number on it. Unfortunately, I see you don't have the receipt. So this alternative is a dead end.
