Beginning with bills issued on and after October 1, 2003, a delivering supplier maintaining a place of business in this State shall collect, from the purchasers who have elected the alternate tax rate provided in Section 5-10 of this Law, the tax that is imposed by this Law at the alternate 2.4 cents per therm rate. The tax imposed at the alternate tax rate by this Law shall, when collected, be stated as a distinct and separate item apart from the selling price of the gas. The tax collected by any delivering supplier shall constitute a debt owed by that person to this State. Upon receipt by a delivering supplier of a copy of a certificate of registration issued to a self-assessing purchaser under Section 5-20 of this Law, that delivering supplier is relieved of the duty to collect the alternate tax from that self-assessing purchaser beginning with bills issued to that self-assessing purchaser 30 or more days after receipt of the copy of that certificate of registration.