Could you just ask you boyfriend to pay it for you? Because looks like you have knowledge on paying it online so there must be a problem in Visa4UK end with your card.
Honeslty, it is really hard to contact the people behind that website
E-mail: UKBAIG.ServiceIntegration@fco.gsi.gov.uk
or:
go to this link:
https://www.gov.uk/contact-ukvi-outside-uk