Reception report was emailed the following day. QSL card with programme schedule arrived on 21 March 2018. Unfortunately the card is not signed and documented with date, time and frequency.
I assume this is a confirmation of a Thai station, but perhaps not necessarily Radio Thailand. Rather it might be Kong Thap Phak Thi Nueng (1st Army Area) in Suphanburi Province which also operates on this frequency. In either case the acknowledgement is a Thai MW confirmation.