"Insinuating" is not the right word.
I agree that there is no need to repeat thanks given a mere sentence before.
I would change "an opportunity" to "the opportunity."
The second sentence is less clear. What are you "assuring" them of? You don't "assure to offer." Perhaps "We owe our success to you and will always provide you with our best service(s)."
(I don't know if you offer a service or various services.)