11.74p off-peak yet charged more 🤨

Ok so im not any EV plans .. I just use my off-peak for EV charging as I use a granny charger. My off-peak is currently 11.74p. Between my off-peak 30 minute slots the price hits as much as 16p or usually 14/15p Instead of 11.74p that I'm contracted for as my off-peak official plan price.

So WHY am I being charged over my 11.74p by as much as 16p during 6 hrs of EV charging. Plus is this happening to anyone else ?? I used to find phoning Octopus a pleasant experience although now im not having the best experience lately. Plus barely do they get back to me.

Thanks in advance.