Why am I being charged for roaming when it's off on my iPhone?

So recently, was on a trip to Asia from the US (home country). Recently, we switched cell phone providers - my old one had free data roaming (low speed) in foreign countries while my new plan charges. I was well aware of this, so specifically turned data roaming OFF on my line settings to avoid using data. I know it was off because after landing, I could see the phone voice] connection active through a local carrier, without a data marker LTE, 4G, 5G, etc.) next to the carrier name. I also did get a local eSIM so I could use data while I was away, and correctly saw the data markers next to that line, along with my data availability going down as I used it. All good so far.

I did also use roaming on two days while I was gone - I received a text, as expected, from my carrier noting I had used a roaming ‘pass’, which on my plan charges me a flat fee for use up to 24 hours, with a new pass purchased anytime I would roam again beyond that period. Still good here.

Got home to find a bill showing 21 roaming ‘passes’ used, along with requisite charges. This would be for almost every day (if not everyday) I was away. I know I didn’t use it - for one thing - the only texts I received from my provider noting passes being started were those two days I used them. Also periodically checked the connections and settings that always noted data roaming off. Bill shows multiple data lines ‘used’ each day, almost all of which were tiny data amounts (.01MB, .02MB and .04MB for almost all).

my carrier is arguing the charges are valid, despite data roaming being off my entire trip? How is it possible that the data is showing used while data roaming is off (ie, while the data pipe is, theoretically, at least closed/off). If data is coming through the line, what does the data roaming setting actually do?

trying to figure this as I know I shouldn’t be garnering charges, but also so I know how to prevent this in the first place. I purposely didn’t turn the line off because I did want access ‘in case’ - also, there are certain things I could do with the line that didn’t generate charges (ie, I can receive SMS for free internationally - I only get charged if I send one outbound - I know this isn’t what they are charging for as the bill notes none of these items - just those very low data lines).

Appreciate any insight.

[Re-Titled by Moderator]