One word of advice:
Don't
I have personally overseen hundreds, if not thousands, of these complaints, and none have ever resulted in favour of the complainant.
Bailiff companies will never concede to a complaint no matter how compelling your grounds are. Their trade associations work on the side of the bailiff companies and essentially act as an apologising service.
That is why official advice agencies send you there. It is designed to wear you down until you eventually give up your complaint.
The only way to get a bailiff company to pay redress is to take legal action against the council or authority for whom the bailiff company is acting. That also takes the bailiff company out of the loop entirely.
Check whether your complaint or claim is winnable. Make a written first-person account of the events leading up to the bailiff action. Collect your evidence and then,
Contact me for a telephone consultation, and you can start action straight away.