Formal Legal LEtter

Hello to all! I'll be very thankful with the person who tries to support me with this letter. I had to write it for work and it has to be very formal but im not sure it's ok. Could you please take a look ?

Dear Sirs:
Taking as reference the recent e-mail exchange between L. M. for XX and K. P. for YY, we would like to notify you of our problems in relation to one of the specialists Your company provided, Mr. AA. Since the 1st of October Mr. AA began working from his domicile and eventually reported for his work, whilst from the 10th of October he totally abandoned his job without making any effort to contact XX and offer a satisfactory explanation for his absence. Additionally, Mr. AA has not returned XX’s property in his possession.
For these reasons we consider that a substantial breach of the Agreement between YY and XX dated DD/MM/YYYY, its Addendum and the connected Statement of Work, dated DD/MM/YYYY, was committed and we therefore expect that, based on Art x of the Agreement, the Statement of Work, which regards the role of Mr. AA will be terminated and no replacement will be given in relation to that role.
We would also like to insist on the return of XX’s property in possess of Mr. AA.
We would greatly appreciate you giving this matter the maximum importance.
If, as per clause x of the Agreement, XX’s property is not returned in 15 days, we will invoice YY. for the amount of XX$ , representative of the property's value.
We feel it our duty to point out that XX will maintain its rights and deriving legal actions against YY for any other prejudice that XX might suffer either from the current situation or from any other breach of the existing contracts.

Yours faithfully,

[Anglika]

As with any serious legal matter, this letter should be vetted by a legal expert.