How can you stop grinding your teeth at night if the mouth guards did not work?

Mouth guards aren't intended to stop grinding. They are to help get some pressure of teeth and protect them from damage. Talk to a dentist and they will help get the right guard for you.

If you really can't get on with a nightguard then you might consider botox injections to your masseter muscles. But bear in mind that botox treatment is considerably more expensive that using nightguards.