Internet/calls not working (new SIM)

Hi, and sorry for writing in English, I am new in France!

I just bought a La Poste SIM card with a 'forfait' online. I got the SIM card, and my phone recognises the internet settings (so no problem with that). I also got the SMS with my phone number, so I think the SIM is activated.

But whenever I try to access a web page, it redirects to a page of SFR, and whenever I try to make a call, I cannot (the message says something about recharging).

Could anyone please help me solve the problem? You could reply in French if it is easier, I can understand :)

Thanks in advance!