"I am not sure why they have not arrived. ... " (more) If they arrive in the next few days, please let me know. If they have not arrived in 6 days I will send a replacement free of charge."
"I am not sure why they have not arrived. ... " (more) If they arrive in the next few days, please let me know. If they have not arrived in 6 days I will send a replacement free of charge."
"I am not sure why they have not arrived. ... " (more) If they arrive in the next few days, please let me know. If they have not arrived in 6 days I will send a replacement free of charge."