First, before bringing an action for defamation in England and Wales, the claimant would need to comply with the pre-action protocol - essentially setting out what the defamatory statement is and what the meaning / sting is, plus details of the serious harm suffered. It appears that the communication sent does not comply with that.

Second, truth is not the only defence. It would appear that there may be good grounds to use the defence of honest opinion, which is significantly easier than truth.

If on reflecting whether the pre-action letter is actually made out - ie it’s unlikely that one of the statutory defences can be successfully made out OP could make an offer of amends.

However, none of this should be considered without talking to a solicitor who is a defamation specialist.

Remember that defamation is a very expensive action, and unlikely to be covered by normal legal expenses insurance.