Dear....

Further to our recent correspondence.

I can confirm that my understand is that your query is as follows [outline what the dumb bint asks]

In several telephone conversations with you this afternoon I have provided you with the following information [outline what you told the dumb bint]

I hope this clarifies your enquiry. If you do have any further questions, please confirm via return email and I will endeavour to answer them in full.

Kind regards,

[your name here]