Argos complaint: Gents Bicycle

I ordered a gents bicycle from Argos a few weeks ago . It arrived at their outlet place with-in Sainsbury’s last friday , where upon I arranged to have it collected .
I got round to building the bicycle on wednesday when I woke on thursday morning I noticed that the rear tyre was flat . I pumped it up using a regulation bicycle pump . After an hour or so the tyre was flat again . I have contacted Argos twice and on both occasions they said there is nothing they can do until the covid 19 crisis is over . I understand this , but I have a bicycle that is of no use because of the flat tyre ( it is probably a faulty inner tube ) as I have’t had chance to ride it yet .
I was told that I could repair the fault myself , my arguement is that the product is not fit for use . The two people I chatted to on the Argos on-line portal refused to budge or to help me any further .
I asked if they could send me a replacement and I will store the defect bicycle or to refund my money to which they refused .