Why don't you just discriminate them and switch to solomo? solomo
pro is cheaper (especially for calls to Italy, which only cost € 0.09/min to fixed lines and € 0.29/min to mobiles) and they accept credit cards without restrictions. You can even import your existing T-Mobile number and solomo pro includes a free VoIP-account, through which you can receive calls on your German mobile number for free (no roaming charges) all over the world (of course only if you use VoIP).
If you order through
this link you'll even get extra credit of € 5.