If you have just received a letter from Sandra Gillissen Verschage apologising for the cock-up of Mourant sending out letters instructing you to either sell or transfer ESPP shares, call ASK HR immediately if you really did want Mourant to retain trusteeship of the shares (and to cancel any sell/transfer instruction you were instructed to submit). They will need a cancellation instruction in writing (e-mail will do, but no e-mail id was given on the letter).
Ron