Question about my 9 yr old

My step son is 9. He is at our house every other week for a full week. Recently he started telling lies,not bringing homework home, not listening, not doing as told, etc... A few months before he lied and his dad whooped him and we thought that was the end of it. Well then all this started. We grounded him from TV and video games for a week. But then he lied again. And wasn't doing as told so he got grounded again and I took all toys out of his room. He has a chore chart on fridge with daily chores. He hasn't done any this week. and last night when I started doing his chores he got the remote and turned it to cartoons (guess he thought he was going to unground himself). after I got baby to bed I asked him why he hasn't done chores he said his stomach hurt Monday and head hurt yesterday.. He lied because he was up playing with his little brother and that was first I heard of it... What other punishment can I give? He's already grounded and already has toys out of his room... Am I supposed to make him write off? Do planks and push ups? I need something creative that will work because being grounded and no toys isn't bothering him none. any advice is welcome.. Thanks in advance..