Oh I'm sorry I misunderstood as the following led me to believe you paid cash, rather than doing it with a credit or debit card as you must have used to do it online.
When I requested a refund the CSR told me it was impossible to upgrade a miles flight using cash and it was probably a mistake
If they say this segment is non-refundable then I'm afraid that is the case. When you upgrade online ISTR there's a box that you have to tick saying you agree to the T&Cs of the upgrade. I think it says in there that it's non refundable (though I can't remember as I've only done it once this way).
PS - I see Dilly has asked you for the info so he's going to be your best bet for getting more help from here