Ref: (nature of your complaint/reference number)
I am writing with regard to the above complaint. I wrote to you on (date) and (date) asking you to do (describe the action you asked them to take) to resolve this complaint.
However, your attempts to resolve the problem have not been satisfactory and you claim that there is nothing more you can do to help me.
I feel that we have reached a deadlock situation and, therefore, I am left with no alternative but to take my complaint to the (name of) ombudsman.
Please issue me with a letter of deadlock so that I may refer this matter to the (name of) ombudsman.
If I do not hear from you within 14 days I shall assume that you are in agreement that this case has reached deadlock and I shall refer my complaint about you to the ombudsman without further reference to you.