I need to upgrade my account from Hobbyist to Trader. I had already paid Eur 79 for my Hobbyist account. Yet, when I try to upgrade to Trader, instead of having to pay just the difference, I am asked to pay the full Eur 199. This is wrong. I should be asked to pay Eur 129 given that I’ve already paid Eur 79 before. Please tell me how to proceed.