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 hereand they can let you know what the problem is.
Have you requested to move over your number to a new SIM? If you're getting this error message then your transfer must still be in progress, just sit tight and this should be sorted for you soon. If your number has already been moved then it's best to get on to the care crew here
Has your number been transfered over yet? If not then just give it another little while and it should sort itself out. If your number has been trasfered over and this message is still coming up for you, then it's best to get in touch with the care crew here
Has your SIM been activated yet? If not then just give it a little time and it should sort itself out. If your SIM has been activated and this message is still coming up for you, then it's best to get in touch with the care crew here