Why hasn't my domain been verified?

Hello,
I added a new domain to my account, and added the TXT record to the DNS. As expected, it immediately showed as pending verification.
However, it's been like that for a few days now. I haven't had any notification of any success or failure to verify, and the status is still pending.
Anyone any idea how I get this verified? The other domains I've added were verified within a few hours.
Thanks