apple site will not allow me to purchase iPhone

Tonight and last night I went into apple.com to purchase a new iPhone. I selected the model, then BUY, the color, the memory. I provided the model and condition of my trade-in, then selected BUY instead of Trade-In. I selected my carrier, then chose NO on the repair coverage. I clicked on CONTINUE. I put in my wireless number and my TMobile PIN. I receive a passcode on my phone, which I enter. Then I get the dreaded message: "You recently made changes to your T-Mobile rate plan that are not yet active. If you want to continue with this purchase, contact T-Mobile Opens in a new window

and ask them to activate your plan immediately or cancel your rate plan change. Then, you can come back to apple.com and complete your purchase." I spent over 30 minutes on the phone with TMobile's support yesterday. There is nothing new in my account - it hasn't changed in over a year. They claim the apple site is to blame. Meanwhile, I cannot purchase a new iPhone. I'd like to have it before my vacation, but I'm no longer hopeful that that will happen. Assistance would be appreciated. Thank you.

[Edited by Moderator]