Hello moffit,
There are a few possible issues, but they should all be easy to fix if it is the case. First, it may just be the charging cable. Cheap, third party, gas station chargers are not very good, nor apple MFI certified cables, meaning they can possibly damage your phone or throw its battery cycles out of whack. If that is not the issue, the repair place you took it to could have broken the charging port by accident. This would hold them reliable, but it is a fairly ''rare'' occurrence. Lastly, it may just be the battery not wanting to charge. This would also be the repair places fault, but it is not likely.
Hope this helps!