It is not just de-monetisation that devalues currency, it's also inflation and exchange rates.

I am currently having a short break in Istanbul, Turkey.
When I was last here in April 2019 there were about 7.5 Turkish Lira to one British pound, now there are about 19, and the cost of a beer has increased significantly.

Over three years the 600 Turkish Lira I kept in my travel bag devalued from £80 to £32.