Make sure you entered the proxy address and port under HTTP AND HTTPS. The payment page is HTTPS encrypted.
Just got Premium for $119 from India. Took me a while to sort the whole proxy thing out (also Chrome on Mac), I had the same issue, but saw the solution on the ozbargain page.
Just watched a bit of Nets-Wizards on my Galaxy Note 3, and wow it's amazing even on my awful net connection.
i can't see the HTTPS area to enter the proxy, wont let me submit the payment form.
is the https area still in the change proxy section?