Changing username creates a new user entry in DB

[tb94]

Describe the bug
When a user changes their discord username, the bot cannot find them in the database.

To Reproduce
Steps to reproduce the behavior:

1. accrue points in a server
2. change discord username
3. /balance shows new balance

Expected behavior
A clear and concise description of what you expected to happen.
user snowflake should be stored as an ID