I'm afraid that right now I already got an offer to work for (ชื่อบริษัท).
I feel good in hearing that you're interested in me.
Hello, my name is .... I call you because of the job offe from your company. Actually,I have to say that I am deeply regret that I cant take the position you have gien to me because I decide to accept the offer from another company.
I am so sorry if I have made any inconvinience to your company. Thank you very much for the opportunity.