I sold my Chametz this year as every year and I realised that I had sliced bread in the freezer. Can I use it now (after Pessach)? I did sell EVERYTHING I had food wise to a non-jew. Please advise! Thanks

The Chametz sale is not a mockery, it is a real sale. As such, your Chametz wasn’t yours during Pesach and therefore the prohibition of eating Chametz owned by a Jew after Pesach does not apply here. It is true it is better to burn Chametz before Pesach rather than selling it however since you have sold it you can use it.