JEK Industries, Inc., was given an unemployment compensation rate of 5.7 percent on August 18, 1977. On September 19, 1977, JEK was advised that its compensation rate was 2.7 percent. This last notice was erroneous and the mistake was not discovered by the Department until 1979, and it notified JEK of its errors on July 19, 1979.

The findings of the referee, which were adopted and approved by the Commissioner, established that under the statute (Minn.Stat. § 268.06, subds. 19,20) JEK was obligated to pay the difference between the established rate of 5.7 percent and the billing rate of 2.7 percent for the year-1977. We agree and affirm the order of the Commissioner.

We note that the present record does not dispose of the question of assessable interest. We conclude that interest can only be charged to JEK from and after July 19, 1979, the date of notice of error. Further, no statutory penalties may be assessed against JEK.

Affirmed with modification.