Change currency in Craft CMS using the Charge plugin
Developer of Charge here.

It sounds like you could be running an older version of the Charge.  There was a display bug on the overview page that would set the currency symbol incorrectly for some setups. 

This is fixed in the latest versions, so make sure you're running 2.2.0 or above. 

Note - this fix won't affect any previously recorded payments that were in a non-default currency, but this is purely a display bug on the overview page - if you go into the detail view for the specific Charges, they'll be correctly showing the relevant currency, and all the details visible to the end-customers and on Stripe will also be correct.