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There is often a call plan in place which can restrict internal dialling.
I would start by logging into Skype, and update your contact details, and check the account balance matures the credit you have cited.
Are you able to make local (in country calls) or do you have the same problem calling in-country as you do international?
In terms of when you dial french (country code 33), are you using +33 or 0033?