Composition limit under Section 10 crossed - Goods and Services Tax - GST

Sir, One of my client has opted the composition scheme under section 10 of CGST Act and forgotten to give option to come out from the composition. The authority has levied the tax as per scheduled rates of 12% and 18% on taxable goods but denied ITC as per Section 18 of the CGST Act . 1.Pl clarify whether the client is eligible ITC during the period in dispute as per Section 18 when the client was not opted from composition to regular taxpayer?