15. A provider who fully reimburses a client the sum that the client paid for a telephone service referred to in section 8 must also reimburse the tax the provider has collected for that service to the client.
In that case, the provider may deduct the tax 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 end of the period during which the provider reimbursed the client.