Normally, plan provisisons rule, assuming they conform to any limitations required by federal law.
From your statement, it appears the applicable plan provision is the plan-imposed limit of paying "small" benefits only if less than $20K. That type of provision might be unusual for a 401(k) or profit-sharing type of plan, but it is permitted. Assuming I understand your facts (which is not necessarily a good assumption), you can ask that the plan be amended to permit your distribution.
BTW, what do you mean "frozen"?