Stuck on activation lock, won't let me log in with my Apple ID. Macbook Pro '16.

You should contact Apple directly, especially since it's a refurbished Mac.

World-wide Apple Support -

https://support.apple.com/en-us/HT204169

Support by phone, email or chat -

https://getsupport.apple.com/

Apple Support by Twitter -

https://twitter.com/AppleSupport

ASC - Late 2012 Mac mini, macOS 10.15.5; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.5.1; iPhone 8+, iOS 13.5.1; TV 4th Gen, tvOS 13.4.6;  HomePods, audioOS 13.4.6 and Airport Express w/ Airplay 2

See Turn off Activation Lock https://support.apple.com/en-us/HT201441. Sometimes Apple Support can help you with activation lock. But, note that if 

(1) you can't use the instructions in the above document to. remove the activation lock;

(2) you, or the person you acquired your device from, doesn't have the receipt from an authorized Apple seller for the purchase your device with the device’s serial number on it;

(3) you don't have a court order instructing Apple to assist in the provision of access to a decedent’s information from the deceased person's accounts; or

(4) you can't obtain the needed password from the person you acquired the device from, 

then the device is useless to you.

If you want to contact Apple support to deal with your problem, see the support links below. Alternatively, if an Apple Store is open in your area, then you can go there to deal with your problem. In this case, you can make a genius-bar appointment (https://www.apple.com/retail/geniusbar/) if you want.

Get a call from Apple support to help solve your problem using this

link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362

Apple ID Support https://support.apple.com/apple-id

Apple ID account security for country-specific andregion-specific help https://support.apple.com/en-us/HT204169

Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best support option. 

Sorry to give you bad news but I had that same issue with a refurbished macbook pro 2019 which was bought at apple.com. 

I contacted apple support, form submitted with invoice/receipt proof of purchase, however, it was denied by apple 2 times. Then I got contacted by an Apple Retail Executive Relations person on response of an email I sent to Tim. What helped me was the fact I was inside the 14 days return policy which I did and then apple replace it for a brand new macbook pro 2020.

Apple support wont deactivate it. Sorry.

That isn't the experience that anyone else has reported in these communities.

You'll see. Follow the proof of purchase process and you'll see their poor response.

Im glad that apple executive retail relations team reached me directly and gave me a quick fix for this issue.