Sprint review: return 2 phones within guarantee time

My name is Yaimaris Perez Cuenca. I
bought 2 used Samsung Galaxy S8 + at Spring Store Gresham Station (681
NW Gresham, OR 97030) on July 14th, 2019 for $499.98. I paid full
amount for them. I activated 2 lines and I had to cancelled this
service after 4 days because I didn't have internet connection. I went
to this store on Saturday, July 19th, 2019, the cashier, named Abel
Pasillas, told me he could refund my money because we are within the
30 days policy return (only 6 days). Today, Saturday, July 20th, 2019,
I went again to this store to get my refund and for my surprise, the
cashier who attended me today, she said they can't refund my money
because I cancelled my service 2 days ago and they don't have any
account history. They state I need a refund kit to return my phones
online. They gave me a customer phone number (888 211 4727). I called
that number and I spend more than 2 hours over the phone with
different persons. Also, they spoke 2 times with the cashier and
costumer services state they can't send me a refund kit because I
wasn't in a lease. I paid full amount for this 2 phones. I spoke with
Gredigan Wade, General Manager of the store and he said the same. They
can't refund my money because they don't have my account history.
I don't really understand why I can't get my refund. I just want to
return these phones and get my money back either in the store or
online. It is my right as costumer to return these phone if I am not
satisfied within the time stablished.
My phone number is [protected] if you need it.
I hope you can help me to get my money back.