I recently purchased a PAYG SIM and opted for the "top-up by £5 receive £10" in the sales journey. I've since topped up by £10 because I would like to take advantage or your Big Data and Texts tariff. However the Change Tariff page tells me I have to top-up again to be able to change my tariff. My current balance is £17.85 and I topped up using my credit card over an hour ago. Can anyone help?