The grantee shall file with the Clerk of said City, within three months after the expiration of the calendar year, or fractional calendar year, following the date of the granting hereof, and within three months after the expiration of each and every calendar year thereafter, a duly verified statement showing in detail the total gross receipts of such grantee during the preceding calendar year, or such fractional calendar year, from the sale of gas within said City. Such grantee shall pay to said City within 15 days after the time for filing such statement, in lawful money of the United States, the aforesaid percentage of its gross receipts for such calendar year, or such fractional calendar year, covered by such statement. Any neglect, omission or refusal by said grantee to file such verified statement, or to pay said percentage at the time and in the manner specified, shall be grounds for the declaration of a forfeiture of this franchise and of all rights of grantee hereunder.