What is wrong with this "thank you note"? I strongly feel its wrong

[Englishholic]

We would like to thank you for being our privileged customer and giving us the opportunity to serve you.
We owe our success to you and assure to offer our best of services. We once again thank you for your valued patronage.

(The above is a text/the above-mentioned text/the text mentioned above) is text suggested to us by one of the graphic designers who is designing a thank-you note for us. I'm unable to tell what is (wrong 'with' instead of 'in' here is better) " I think It's wrong" I feel Its wrong"....hope this helps!!!

[konungursvia]

Yes, our best of services was, to me, the only thing that was wrong.

You could say "the best of our services."

[wannabelean]

Thanks guys!