Respected Sir,
first of all thanks for your help. Your help in the time of the flood was indeed like a help from God. And you indeed is a God. I and my family were in a severe situation in the flood. No food, no water, no clothes, no house, we lost everything. But your help came to us like a gift of God. Now we have food, water, clothes and a small hut.
Thank you Sir for your kind and generous helping. May God bless you and your family.
Yours sincerely

(You can fill the cross with this year or the years before. And you can fill the dash with the name you like)