Do you think I’ve been overcharged here ?

[C2019]

Hi everyone
Not sure if anyone can help but today I posted 3 items and I post the same items on a weekly basis. I paid on my card and looking at the receipt just now I think I have been overcharged.
It was sent as follows :
1st class signed for
Item weight -0.533 kg
(MP) - Medium parcel.

I was charged £8.05 for this.

Now normally when i post these they are £5.55 by the lady who I usually see but she wasn’t in today.
Having looked back at my old receipts it seems she puts them through at (SP) small parcel and they are always the same weight.
Perhaps that’s why I have been overcharged because of the medium parcel instead of small parcel?

Package dimensions are 40cm x40cm and every time I have posted before at this size it has always been put through as SP. Would I be able to go back tomorrow with my receipt and previous receipts to get my money back?

[Woody Guthrie]

40cm x40cm

The maximum dimensions for a small parcel are 40cm x 35cm x 16cm.

[C2019]

But I’ve posted items before at 40x40 and they always get put through as a small parcel

[TrueBlueTerrier]

But I’ve posted items before at 40x40 and they always get put through as a small parcel

Then, sorry to be frank, you have been lucky before.

Royal Mail asks the Post Offices to be strict on the size of parcels, but the post office manager has probably let them through as you are a regular.

The problem is you now think you have been overcharged when it's actually the opposite. Even if the regular lets you go through with the oversize parcels in the future, if you are selling, then there is always the chance the receiver will get a surcharge notice (which is the missing postage plus an admin fee) and it may negatively affect any feedback.

Also once Royal Mail put all parcels through a sorting machine, which is the plan, then they will be rejected and surcharged automatically.