Every mutual insurance company or association admitted to Missouri under the provisions of sections 379.205 to 379.310^* shall annually pay to the director of revenue a tax upon the direct premiums received, whether in cash or in notes, in this state, for the insurance of property or risks in this state at the rate of two percent per annum; provided, that such companies or associations shall be credited with cancelled or return premiums actually paid during the year in this state.