Demand u/S 143(1) AY-2020-21

Filed return on 22/08/2020,in time. Demand came on 8 April 2021. Total income 13.431 Lakhs, & they agree. Tax Liability 185765 & they agree. Interest 1577/-&they agree. Prepaid tax 187400 & they agree. Yet they say tax payable 28500/-. Why so? I don't find any reason & the notice also does not indicate. Immovable property was sold. Purchaser deducted 1%.& they deposited 28000/-on July 31, 2020.Form 26 AS confirms this. I have no hesitation to, but, they must tell me what for it is? So that I may be careful in future. Can you throw some light on this issue please?