Dear SWD recently my inventory got cleared because the staff says I griefed and got banned but I don't remember griefing or got banned so I want to know when I got banned and the reason and if I did not grief but got banned for a other reason then I want my items back

An Admin already told you that you were banned for griefing.
Staff have access to the ban logs to there is no point in saying you weren't.
Just deal with the fact you lost your inventory full with lapis, diamonds, bedrock  and other stuff

which were stolen from chests that you griefed.

he said his inventory was there before he relogged and it got cleared so idk

Yes, The Admin saw that they still had items from the chests that they had griefed so he reset his inventory. Seems completely reasonable.

You were stealing items and clearing your inventory is a reasonable punishment.

Fortunately, you can still play on the server. Learn from your mistakes and try not to do this again.

Have a good day.