You may not be able to call Thai Airways Airlines for a variety of reasons. For example, the airline may not have customer service available due to high call volume, technical issues, or other unforeseen circumstances. Also, some issues with your phone or phone line may prevent you from making a call. However, you may be able to call the airline back if this happens. Also, consider contacting them through their website or social media channels.
Source: https://www.qxbooking.com/flight/thai-airways-flight-booking