Indeed, and similar (or even non-availability of higher-demand supplies, at any price) seems to be true in many countries.Tariffs based on maximum demand are the norm in France - a 60/80/100A supply would be ruinously expensive.
Do I take it from this that the generation, distribution and sale of electricity is not a viable profit-making activity? That's the only viable explanation I can think of for the rather unique situation in which a 'supplier' seeks to limit it sales and/or charge more to those who want to buy more of their product!
Kind Regards, John