Welcome to Vodafone Community
May I ask you to please clarify what your trying to pay for.
Sometimes clearing cache and cookies of a browser can help and or try another Browser.
Here is Vodafones help pages.
Customer services on 191 or Live Chat can access your account and also help you further too.
Current Phone > Samsung Note 9 _512Gb > Model: SM-N960 Hybrid-Duos.
Samsung Gear s3 Frontier Watch.