Airtel — international sms usage wrongfully charged

Website:

www.airtelin

In my current month bill i see that ive been charged for 78 international sms which ive absolutely no clue of sending. These messages appear to be to the same international number:[protected] which in unknown to me. The messages have been sent multiple times on days.
I'd raised a complaint via the local airtel store in pondicherry (Mg road) on 14th may 2018. Till date this hasnt been resolved.