Sadly, as you have just found out the Pico cage is not suitable for hamsters. It is too small in floorspace and too tall. I wonder if you can return it and get your money back.
Finding suitable cages has become a bit difficult since Brexit/covid but I did create a whole thread about UK cages, with links were to buy or look out for any of them 2nd hand on gum tree, facebook marketplace, preloved, freeads, shpock etc.
UK Hamster Cages 2021
Hope that helps.