I've previously enabled TFA for my twitter account successfully.
Yesterday I received an email saying my phone number has been removed from my twitter account: " Login verification has been turned off for your account. Add a phone number to turn it back on. To further protect your account, @josephhinvest, we now require you to have a phone number in order to use login verification. Since you removed your phone number, login verification has been turned off for this account. To turn it back on, simply add a phone number...
"

I thought it was phishy so logged into twitter manually and yes sure enough, phone number gone.
Tried to add it again and it fails with a message "not supported at this time".
My number is an 021 number currently with Skinny. However when I checked again the number had been added, but when I try to get the verification SMS sent, I receive nothing. Any ideas?
Thanks

Edit
The text of the error is "The phone number you provided is not supported at this time."
I am supplying the number in format +6421xxxxxxx, but have tried local version too.