Accusing people on this app of cheating is considered taboo. You are supposed to email somewhere I think and they will check. There is probably a link.
However, this *is* kind of a special circumstance and if you just post the game we can look it over for you and let you know if its worth submitting it for a look. The thread might get closed first, but its worth a shot. Post the game.
Your opponent was not cheating. You just had a blunderful day. The moment you stop worrying about rating and any potential "cheaters" is when you become a better player. This is online chess, and at the end of the day, it is all just a game meant for enjoyment. Cheating, although a concern, is simply a matter of ego on both players. If you are suspicious, report them after the game, and continue on with your day.
I regularly play my friend in person. I got him on this app and the first two games were played in the same way as we do in person. The last two games, it was like he became a grandmaster Jedi! I didnt stand a chance! He obviously denying it but surely there some method I can check?
Thanks