When you have a serious complaint to make, emails are ok, as long as you remember this: Never address your email to one person only.
If you write to only one employee, he or she can use the delete button, and nobody is the wiser.
Instead you should write to as many employees as possible, listing them individually as recipients in the same email message. Always remember to include persons on the top of the firm's hierarchy! Sales persons, marketing and pr, bosses at every level...
Then the delete button will be out of the question, and somebody will be given the task of answering your query.
Good luck! Emeralddragons