“Thank you once again for putting my mind at rest”

"Dear Richard, Just a short note to thank you for your help recently with my VAT registration. You may recall that I was somewhat anxious about VAT and the correct procedures associated with invoicing clients and being invoiced by suppliers in various EU countries. I think your very pleasant receptionist must have detected the worried tone in my voice, because you returned my call almost immediately. Needless to say, you explained everything extremely clearly."