DPD UK review: Breach of data protection act when delivering parcels

I have trouble with my neighbour and it is very likely that I will have to take her to court for hate crimes. I am also involved with the police regarding her behaviour. Last year, I sent a hard-copy letter to DPD informing them that they should not divulge information about me when delivering parcels. I had a response from DPD (ref 00D4KEqrj._5004KYdAqx). I assumed, therefore, that my data was fully protected.

On 11th January, I had a delivery from DPD and on the notes I instructed the courier about the problem next door and not to take any notice of her behaviour (she will shout and scream at couriers not to park near her house and will sometimes ask the courier who the parcel is addressed to and then take photos of him delivering the parcel to my home). A few days later, the neighbour came out when I was leaving and screamed at me not to tell the couriers what I had said. I would like to know how it was that my neighbour knew this. I have another delivery today [protected]). If the courier gives any information to my neighbour about my parcel, they could end up in court.