16. A provider who collects from a client an amount as tax in excess of the tax that the provider was required to collect must reimburse the excess amount to the client, if the client so requests, within 4 years after the day on which the amount was collected.
In that case, the provider may deduct the amount reimbursed in determining the tax for the period referred to in section 12 or 13, as the case may be, during which the provider reimburses the client or within 4 years after the day on which the amount was collected.