Landlord acts illegally/criminally

Tenancy Deposits

I would like to ask for advice from the point of view of tenant. I have a family member who rented a flat from NOVEMBER 2016 until beginning of 2022. A tenancy deposit was paid for, the person wrote twice to landlord and estate agent (who managed property) to request return, no reply. No check out inventory was done. I have since found out, this weekend, that the landlord did not issue the prescribed information whatsoever, nor How to rent leaflet, the deposit certificate was emailed 6 months after start of tenancy, not within the 30-day time limit required by law.
A gas safety certificate was NOT given prior to moving into property, one was emailed 2 years after having lived there
No EICR (electrical) certificate was ever provided
No EPC certificate was provided
Where can my relative turn to for help.
As a landlord I keep within the law, because I provide all necessary documentation within the required time span, EICR, Gas Safety certificates are provided prior to my tenants moving in. So I do not know what tenants can do if their landlord has committed an offence.