There are a few different errors that can come up when you're trying to buy membership. Have a look below and see if you can figure it out:
Remember, when getting in touch with the care crew about an error message, you'll need to include the error.
Have you reported your phone lost and ordered a new SIM? If you have then you need to wait for the new SIM to arrive then buy membership.
It might be that you have not used your phone in quite a while. If you have not made any calls or sent any texts in a long time your number could be suspended or de-activated. Contact the care crew here and they can let you know what the problem is.