I must admit that I've had trouble understanding what "Skype WiFi" actually does. Now that I've done some reading, it appears that Skype has arranged access with some providers (apparently Tengo is one of those providers) so you can use your Skype credit instead of paying the provider directly.
In this case, it appears that the OP paid Skype overhead on top of the Tengo rate for 2 minutes(?) access. Probably the minimum amount is 30 minutes access.
FWIW, the Skype credit webpage says that the access rate is displayed before the connection is made.
Just sayin'...