I think you mean, "I have problems studying. How can I get my money back?" ("Return my money" means you give the money to someone else.) I guess work, family or other commitments have made it difficult to take more lessons. The bad news is, you won't get your money refunded so easily. That's just italki policy when you buy ITC. What I suggest is, find someone (ie. someone you know personally) who wants to use your credits for lessons, book the lessons through italki and explain to the teacher that another person will take the lessons in your place. Your friend takes the lessons and pays you back for using your credits, and everyone is happy.

Do you mean that you had a problem on Saturday? Or a problem with studying?