Cancel my subscription and receive reimbursement

I have subscribed to a mobile number, for my father for a month.
After this I went to the store to cancel the subscription, they told me to call the central, I called the central and they told me to go to the store, after a few times trying to resolve they told me that my subscription was cancelled. Three months later I am still receiving invoices of the cell number, I went to the store and they told me that the subscription was not cancelled and that I needed to call the 0800 again to cancel it. I spent almost 20 minutes waiting for someone into the line and no one answered it. How can I cancel the line and get my reimbursement back?