Taking legal advice will normally cost money, and even then your chances in court are mixed if you haven't explored the available adjudication option with CISAS (and that is free). If you're turning to Citizens Advice, they should point you to CISAS anyway, as a faster, cheaper, and more appropriate route. Search read and follow CISAS customer guidance, think about what outcome you want, and what evidence you can provide for the problem you want resolving. And as the CISAS guidance will explain, you must have raised a formal complaint with the company beforehand.
If CISAS doesn't get a satisfactory outcome, then you are still able to take the matter to the courts.