They should have an official complaints procedure which should be your first port of call. Details should be on their website. My own engagement letters say:
Your rights in connection with personal data
Under certain circumstances, by law you have the right to:
• Request access to your personal data. This enables you to receive details of the personal data we hold about you and to check that we are processing it lawfully.
• Request correction of the personal data that we hold about you.
• Request erasure of your personal data. This enables you to ask us to delete or remove personal data where there is no good reason for us continuing to process it. You also have the right to ask us to delete or remove your personal data where you have exercised your right to object to processing (see below).
• Object to processing of your personal data where we are relying on a legitimate interest (or those of a third party) and there is something about your particular situation which makes you want to object to processing on this basis. You also have the right to object where we are processing your personal information for direct marketing purposes.
• Request the restriction of processing of your personal data. This enables you to ask us to suspend the processing of personal data about you, for example if you want us to establish its accuracy or the reason for processing it.
• Request the transfer of your personal data to you or another data controller if the processing is based on consent, carried out by automated means and this is technically feasible.
If you want to exercise any of the above rights, please email our data protection point of contact (DPO's email).
You will not have to pay a fee to access your personal data (or to exercise any of the other rights). However, we may charge a reasonable fee if your request for access is clearly unfounded or excessive. Alternatively, we may refuse to comply with the request in such circumstances.
We may need to request specific information from you to help us confirm your identity and ensure your right to access the information (or to exercise any of your other rights). This is another appropriate security measure to ensure that personal information is not disclosed to any person who has no right to receive it.
10. RIGHT TO WITHDRAW CONSENT
In the limited circumstances where you may have provided your consent to the collection, processing and transfer of your personal data for a specific purpose (for example, in relation to direct marketing that you have indicated you would like to receive from us), you have the right to withdraw your consent for that specific processing at any time.
Once we have received notification that you have withdrawn your consent, we will no longer process your personal information (personal data) for the purpose or purposes you originally agreed to, unless we have another legitimate basis for doing so in law.