Complaints - formal language

Below you'll find some useful phrases of criticizing and complaining.

I'm sorry to say this but .....
I hate to complain but .....

It bothers me that .....
I'm unhappy that .....
It bothers me that you didn't ask me first.
I'm not fully satisfied with this.

Responding to expressions of dissatisfaction. 

Thank you for bringing that up.
Thank you for bringing that to my attention.
Thank you for pointing that out.
I'm sorry. I didn't realize that.
I understand your concern about ...
I can assure you (that) ...
Let me see what I can do.
Rest assured that .... (we'll give you more time to finish the project.)

What seems to be the problem?
What happened exactly?
I'm afraid it's not our policy to ...
I promise I'll ...
I understand you're upset, sir.
I'm trying to understand the problem.
We're sorry that you had a problem with this product.
Is there anything else I could assist you with?

Each company should have a "complaints policy". It is a must when it comes to proper customer care. The service provider or producer should accept complaints and process them effectively and immediately if he/she doesn't want to lose clients.

There's an example of complaints policy on a company's webpage.
Source: http://us.abrsm.org/en/policies/complaints-policy/

We are committed to providing high-quality music education products and services to all our users. We value our reputation and standing as the UK’s largest music education body, one of the largest music publishers and the world’s leading provider of music exams. We hope you’re pleased with the products you’ve purchased or the services you’ve received from ABRSM. However, if there’s something you’re not happy with, please let us know. We take all complaints very seriously and will do everything we can to put matters right.
There are some things which are not covered by this policy. It does not apply to employees or consultants, or in any situation where we have a pre-existing complaints process in place. If you make a complaint under this policy and we think it would be better dealt with using a different process then we reserve the right to do so. Please visit the relevant sections of our website to find out more about:

Who is this complaints policy for?

• 1. Anyone buying goods or services from us, other than our exams, such as our sheet music and books.
• 2. Anyone using our services who is unhappy with the services provided by our staff in carrying out their duties.
• 3. Anyone who has (or has had) a working relationship with ABRSM who is not (or was not) an employee or consultant, such as an examiner.

Please let us know as soon as possible so that we can try to resolve your complaint quickly. In the first instance you can contact us by phone, email or letter. If we can’t resolve your complaint over the phone, then we may ask you to write to us giving more details.
T +44 (0) 20 7636 5400
E abrsm@abrsm.ac.uk
ABRSM
24 Portland Place
London
W1B 1LU
United Kingdom

If you need to contact us by email or letter, please:

• 1. Give your name, address and contact details, including mobile number and email address where relevant.
• 2. Explain what your complaint is about, including relevant dates.
• 3. Tell us whether the complaint relates to you or if you are complaining on someone else’s behalf.
• 4. If your complaint is about an ABRSM individual, please tell us their name (if you know this).
• 5. Tell us what outcome you would like to achieve.