I applied for a UK Standard Visitor visa early for my seven day trip from April 26th to May 3rd, 2017. I applied four months in advance (on 23rd of December 2016) and received the result after four working days. It was a refusal due to: (picture attached)
https://i.stack.imgur.com/EK9B2.jpg
https://i.stack.imgur.com/FOZdw.jpg

My concern is that I did submit evidence about my educational status (Student verification from university, Absent leave letter from university - both are verified and translated into English) - but in the pack of documents they sent me back with my passport, I COULD NOT FIND THEM. I suspect there might be some mistake or maybe they took them out on purpose, but am for sure they were in my application when I submitted it at the visa center.

FYI, my status is:

I am a student (sophomore - in my second year at university).
have not much income.
my sponsor is my uncle who is so close to me because we were living together for nearly 15 years. My uncle owns a company on his own and gave me 9000$ for the trip. (However, there is no evidence of his income nor letter from him in my application).
I provided my mom's incomes as well (1100$/month).
Can anyone give me advice: Should I apply or what kind of document should I provide them to make myself become more convincing?

Because I can't file an appeal there is almost no way for me to find out what happened with the papers from my university

I am going to send a complaint to VFS centre took over my application via their website because it seems to be the only way to do it. Any advice on the complaint?
https://i.stack.imgur.com/VHKcW.png

My advice would be don't bother making a complaint. There's always the chance you don't get paperwork like that back from whoever you send it to. I've learned to send copies if they are accepted.

Request new verification papers from your uni and this time send in proof of your uncle's sponsorship. I'm not surprised your visa was denied if you didn't send proof of your sponsor. Why not include it to begin with? It's my understanding that proof of finances is a big part of the visa application, and I don't think your mother's matter because it doesn't sound like she can support you.

I'm not sure what you would 'complain' about. No one is guaranteed a visa and you were denied so filing a complaint would seem to be counter productive.

Seems to me that the reasons given in the first image you link are crystal clear. What grounds do you think you have for a complaint?

There is no right of appeal for standard visit visa and you are just wasting money and time complaining or asking for administrative review, as they did nothing wrong. You simply didn't send in required documents, including sponsorship letter from your uncle and evidence of his finances, such as 6-month bank statement. If you didn't enclose photocopies, they reserve the right to retain original documents.
Just reapply and make sure you send in all required evidence.

Complaining probably will not work, apply again.

I find that they clearly explained the reasons for refusing in the paper that you linked. It was not about your Student status, but about the lack of (proven) financial support. If there is no evidence of your sponsor's income nor letter from him in your application, then he is not a "sponsor" in the visa term. There would be no use of complaints. It's totally up to them to decide yes or no, or to request further papers, in the first place.

If you apply again, be sure to include all the documents that they require, from their standard procedure AND from their refusal letter. If you apply from Vietnam, they will be very strict (I know it), you'd better not give them reasons to find faults.

Seriously? You applied for a UK visa and listed that you had a boyfriend and that he could support you in the UK? Why on earth would you do that. Boyfriends are nothing, they have no legal status in relation to you. If anything, that only hurt you.

The fact that you have a boyfriend in the UK gives them more reason to suspect that you want to remain in the UK instead of returning to Vietnam. You need to convince them that you have compelling reasons to return to Vietnam.

We found the UK visa requirements were very strict when my daughter was applying to study abroad. We were recommended to show proof of funds in her own bank account and we submitted several months worth of bank documents to demonstrate her financial stability.