Please rule out first that your credit did not become inactive, as is the subject of this thread or topic! If this is not the case, then I suspect your account may have been compromised or "hacked," which is a different matter. Change your account password immediately!
Online Safety Tip: Change your passwords often!
Where has my Skype Credit gone and how do I get it back?
I think you may need to contact customer service regarding your concern. Just click the link below to see the instructions on how you can get in touch with the Support team ;