1st class signed for help!

[C2019]

I post things daily both to the UK and globally and I haven’t really had many issues at all until a week or so ago when I had to send an item of mine to a lady in the UK. The size of the item was classed as “large letter”, was taped up securely and had do not bend stickers on. I sent it 1st class signed for as I wanted the lady to sign for it herself. She received it but I got an email from her saying the parcel had arrived but sent pictures of the packaging completely damaged on all 4 corners as it looked like it had been shoved through her letterbox, and it was bent in the middle.She told me she never signed for it either so I told her I would check the tracking info to see who signed for it as I assumed a neighbour could have signed for it and tried forcing it through her letterbox themselves. There was a signature and it said “signed for by “clients name”, but the signature was just a horizontal line, literally the most pathetic excuse of a signature that was clearly a “ I can’t be bothered to knock on the door or even fake sign this so I won’t” signature. I went through the complaints channels on Royal Mail and I actually received a cheque for postage costs and the full cost of the item sent. You can’t say fairer than that and they admitted they were in the wrong as they said it looked like the postal worker signed for it themselves pretending to the person and put it in the letterbox.
The lady once again required something from me and I once again sent her a package which followed the same procedures as the first package. Lightning can’t strike twice but in this case it did. I sent it first class signed for and she emailed me once again telling me she never signed for it and that the top corner was once again damaged but this time the items inside were fine . I checked the signature and it was even worse than the last one if that’s even possible. I don’t want to go through the same hassle as complaining again as Royal Mail will just assume I’m trying to get money from them , but I pay for a service and it’s not being done correctly. My parcels have items in that are fragile and could be slightly damaged or creased if dropped or mishandled which is why I pay extra for the postman/lady to hand it over to the owner in person...and if they aren’t in I’m on the understanding that they put a card through the letterbox to come and collect it from the nearest office and sign for it ? Am I within my rights to make a claim again? I would be willing to let this one slide however as at least there was no damaged items this time ... and I’m not usually the type to complain at anything but I spend thousands a year on postage so I give them good business .....what do you think?