Delayed tax repayments

Have had a few client refunds recently which have been "selected" for a security check.
One in particular is causing grief to the client who has acted on advice regarding the date on which repayment issued, as shown on our agents section of HMRC website.
The repayment has of course NOT been issued.
Numerous calls have confirmed the position and the only recourse offered was to write to the Repayment Security Team in Bristol. They do not take incoming calls and no-one can comment on likely timescales.
Has anyone found a way through this "conundrum" or do we simply have to wait, completely in the dark, for the process to run its course.
The delays are one thing, but blatantly misleading information regarding the date on which repayment issued (previously so reliable) is potentially damaging.
Mr T