Smart Pay Deceptive financing Bainbridge Georgia

We bought an iphone 7s from Metro PCS in December. We have excellent credit. The sales clerk suggested instead of putting it on charge card , use "SMART PAY". We could make payments over a period of time, no interest auto withdraw from our checking. We received no follow  up paperwork or emails from Smart Pay . I went to the email address on my bank statements to see what i owed and noticed it is leasing the phone with 11 payments! I called them and was told I had 90 days to pay it off since I didn't pay it off last week I now get 20% added  , have to make the 11 payments and now my $669 phone will be costing me  $1139   Superviser said she could'nt alter the computer since it had already "rolled over"  SMART PAY  REAlly  i SAY smart scam.