GST Liability on Disputed Rent income

As per Notification No. 12/2017, Rent paid on renting of residential dwelling unit for use as Residence is exempted from the levy of GST. It is important to note here that only residential dwelling unit for use as residence is exempted and not for use for office/commercial/ other purpose.

The property in question is a commercial property . 

If you have received rent then definitely you will have to pay GST. If you have shown income of rent and issued invoices then also you will have to pay GST. For the current period you can definitely shift to receipt basis since the recognition of income is doubtful.