02 gobbles up balance when no calls/texts

ANGLICANPAT

Comments or advice if poss please. I keep an old basic no frills 02 PAYG mobile purely for occasional use , so its easy to monitor my charges. Because the last balance went down so quickly , unexpectedly , I checked back and it appeared to lose £3 exactly , twice but I wasnt actually recording my usage , so couldnt prove anything .

After topping up £15 (and getting free 02 calls/texts) this time, Ive recorded all my use, and again the balance has dropped by £3 here and there, and smaller amounts randomly .
Ive got a clamshell, which means if I open up straight after being notified of an incoming text , it shows itself in full immediately . I have had a couple of random 'sex' texts' recently ,I delete these immediately but could I be being charged for them retrospectively in so much as the balance doesnt seem to change immediately after these incoming texts, its sometimes days after, with a legit text or call out of my own inbetween , which is why I cant blame them directly. Any other explanations before I try and contact 02?
ps Im a pensioner and definitely havent signed up to receive any of these messages lol -

Ian011

Send the word 'STOP' to the five digit mobile shortcode the text messages arrived from otherwise you will continue to be charged.

ANGLICANPAT

Is it normal to be charged for incoming calls?

Ian011

You will be charged for incoming calls only if you take your phone to Jersey, Guernsey, Isle of Man or anywhere else outside of the UK.

You are never charged for incoming text messages unless they come from a premium rate number, usually this is a mobile shortcode.

ANGLICANPAT

Ah right . Ok thanks, Ill try that .