7 year old constantly lying

My child is constantly lying and trying to be sneaky. It used to be funny. He spent a full year telling me about a class he had in school that turns out doesn't exist. So maybe we let it go too long?But; now it's gotten bad. He hid letters that were supposed to come home from School. I told him he couldn't bring his 3ds to school so he keeps sneaking it. He prentends it's been in his room, etc. and his new one is sneaking Pokémon cards. He told me yesterday that he forgot his lunch box on the bus, turned out he hid it in the bushes and was filling in with Pokémon cards to sneak to school.I've done everything I can think of. We've talked about lying, talked about how the consequences aren't worth it, grounded him a day for every lie, took away tv, video games, time with friends, made him do lots of chores... everything I can think of. I feel like he understands and we can move on, then he does it all over again.Im really t a loss on how to fix this.... I'd love any suggestions via /r/Parenting http://ift.tt/2cXHh6W