I'm having trouble re-adding a recently unblocked friend.

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About two weeks ago, I blocked one of my friends after we had a small scuffle. However, after talking it out in person, we got back on good terms, and I decided to unblock them. I unblocked them about a week after I had originally blocked them, and was having trouble re-adding them. I had read somewhere that sometimes, you would have to wait 24 hrs to re-add someone who you had blocked. So, I waited 24 hours.
However, I was still unable to re-add them. In the days that followed, I attempted everything. I mean everything. I logged out and logged back in, I uninstalled and reinstalled the app, I cleared the app's cache, I tried to get them to add me first, and even contacted support (who never responded). This forum seemed like the next most logical place to go. It has been about a week since I unblocked them (3 weeks since they were originally blocked) and I still can't add them. Any help with this situation would be appreciated.