I don't doubt the letter/email exists; but a cut and paste on a web forum from a third party not connected with the correspondence is no evidence whatsoever.
BASSAwitch has the correspondence, is directly entitled to see the accounts and is in contact with the Certification Officer. They are the party best placed to take this forward; it would be good to see other Unite/BASSA members supporting their former "comrade" but I suppose "brotherhood" only goes so far.
Until we hear back from Bw, there is little to be gained from private individuals pursuing this.
I would still encourage those who do have a vested interest to contact the CO directly using the link below and support transparency, so that it is clear to members exactly how much is received in BASSA subs, what the reps get paid, and to assure them that an independent audit has been properly carried out which demonstrates no potential for fraud.
Certification Officer - Complaints
If, like the refusal to view the BA accounts, BASSA members are content not to see information to which they are legally entitled, then that is a matter for them, and they can keep sending cheques into a black hole.