Tax collected but not paid triggers compulsory remittance, show cause notice, interest accrual and adjustment or refund mechanisms. A person who has collected amounts representing tax and not paid them must immediately remit those amounts to the Government irrespective of taxability of supplies. The proper officer may serve a show-cause notice and, after considering any representation, determine the amount due; interest accrues from collection until payment. Paid amounts are adjustable against tax liability for the related supplies, with any surplus credited to the Fund or refunded to the person who bore the incidence, who may apply for refund under refund provisions. A requested hearing must be granted and the officer must issue a reasoned order within the prescribed period, excluding any judicial stay.