Same case with you when I went to Thailand on 9th April.
Data roaming is off, didn't make any call / pick up call / SMS, data is off. Get charged RM38 as well.

Call to CS and keep telling me the same thing "here state you use GRPS data...etc", change my tone a bit only they willing to make a report.

Last year October I went to HK with exactly same setting (didn't turn on airplane mode), but didn't get charge.

I guess Celcom change how their setting this year to become once you've connected to ANY network in oversea, they will charge the RM38, but just my guess anyway.