I very rarely suggest calling the DOL because it is almost always avoidable , but this may be one of those instances where it is appropriate. The way they are operating the plan effectively restricts catch-up contributions to highly compensated participants who can hit the $18,000 limit while still restricted to 15% of pay per payroll. That is just wrong and needs to be fixed. If you are getting nowhere with them, call the DOL. When they get a participant complaint, they have to look into it. When the DOL comes knocking, things like this will get fixed real quick.