I was Lucky few years ago, I was in Paris being bought a Tango fair, called AC and asked about the upgrading with SSWU. The first person on the phone wouldn't put me on the upgrade list and wanted $500 extra for upgrading to T+. I thought it's not worth. But I called later at night and a different person told me the fee is only $70 for T+ but after telling him about my adventures with AC he upgraded me for free to a higher fair for free^

If you can be nice some times you can get it