I sent a letter to Qui Minnan at the following address: Ren Yu Lan, 491 South Chang'an Road, Xi'an 710061,China but my letter was returned to me with the message that my letter could not be delivered, why is that and should I try again?

Would you please show me the correct way to Address a letter to the UK. a visual example would be excellent. The reason i ask this question, i recently posted a letter to the UK. from Hengyang City and the letter came back to me, i was forced to pay postage again which i think is utterly unfair and i want to make sure this does not happen again.
Please this is urgent.
Thank you.

Hello, my letter was delivered to 心巢御园后面洁丽干洗店自提点 on Jan 26, but because of Lunar New Year, the recipient had returned to her hometown. The staff of the store then brought the letter to 重庆九龙坡区心巢御园后面门店驿站 due to New Year too. According to the recipient who went to collect it, the staff at the 驿站 said that the registered number is not common so they do not know where to classify it in the system. Hence, the registered letter does not exist in the system now. The staff were not willing to make the effort to find it either. I paid for it to be registered, and it wasn't even registered into the system when it was brought to a different place!? What can be done for this situation and how do I get my letter delivered into the hands of the recipient? The recipient went to the 驿站 again today (March 9th) and told me that there was a change of staff. The letter is still not found!