charge one year after i give phone and sim back

I buy phone and sim card from t mobile,and I don't like after 3 days I give them back but I see my accout after 7,8 months they charge me every monts 90 $ some time 60$ when I go to office they ask me when u give us phone and sim back you don't dactivate your sim,thats robbery because they take sim back from me so they have deactivate not me,i need my money if some one can help me thx so so much