We/ regret/ tell/ you/ your request/ tax refund/ reject

A. We regret to tell you that your request for a tax refund has been rejected. 

B. We regret telling you that your request for a tax refund has been rejected. 

C. We regretted to tell you that your request in tax refund had been rejected. 

D. We regretted to have told that your request for tax refund was rejected.