Had encountered same experience dropping every calls. It was during NV upgrade from a nearby tower. What you can do is find out which tower your connected to, call Sprint and give them the site ID from the sponsors map. 3 weeks seems too long, mine lasted 1 week, after several calls to Sprint it was fixed.
Also, Sprint customer service cannot fix this issue, it has to be escalated to a trouble call to a different department that will look into this issue.