Hi Umaiyaal A
Thanks for reaching out to Microsoft Q&A.
did you receive the confirmation email after your sign-up for free trial? It looks like your account is yet to be activated with free trial, hence it asks your card details everytime.
You can reach out Azure billing and subscription management team by creating a billing support request. Billing support request via Azure portal is free for all Azure customers and doesn't require a paid support plan. Please select 'Billing' under 'issue type' while creating the support request.
Please 'Upvote'(Thumbs-up) and 'Accept' as answer if the reply was helpful. This will be benefitting other community members who face the same issue.