UK Visitor Visa and 2x Tier 5 refusals [closed]

Sorry this is a long one.

I have previously studied and lived in the UK for 5 years. I returned to SA after my studies where I have been living and working since my return from UK.

However, in 2015 I decided to apply for a visitor visa to visit old friends....After the death of my mum, I needed a break. Here's where it all goes pear shaped.

Immigration refuse my Visitor visa on the following grounds:

1. I did not prove to them that I did not overstay previously (but they told me that Home office said I left UK in 2005...which DID)
   I misplaced the passport I left the UK with and never thought of keeping the plane ticket either. As these documents would prove I never overstayed. Surely the airports could confirm my return to SA. Immigration say they have no record of my return to SA. (how about an interview)?
2. They said I made an application at the Home office UK in 2012,
   which is definitely untrue, and I proved this by way of payslip and letter from my current employer here in SA and also suggested they check my cctv at work.
3. I do not have any family commitments to return to SA
   Well, nowhere on that application form does it ask about what responsibilities you have to return to etc. In my admin review I gave a list of responsibilities I had to come back to at the time. Firstly I had a permanent job, I had just lost my mum and I have the house to look after. I was also taking care of my niece who suffers with schizophrenia Dr letters were submitted with that application.

I was so disheartened, I did not think to apply for an administrative review

Anyway, a year later, I get an offer to do support work in the UK, I apply for a Tier 5 visa with my friend as we were both offered the job. We BOTH did not submit evidence that we have previously done support work. Her visa is issued to her and mine is refused because of the following.:

1. I did not raise the issues of the 1st refusal.
2. I did not submit proof that I can do the job.
3. And I still have not prove that I did not overstay.

I did not raise the issues as I assumed this was a different category and nowhere on the application did it ask for this information. I do have a certificate from a Disability course I did through grass roots UK, however I did not submit this at the time, my fault. But my question is, why was friend not asked for this proof?

I then apply for an admin review, and showed the certificate, an affidavit stating that the passport was lost.

The review upheld the refusal because I was not allowed to submit that evidence to the review, but suggested I reapply, which I'd did. Only to be refused again. What a waste of money. The reasons for refusal.

1. The signatures on the certificate are not original.
2. I did not submit a description of the job I'm going to do.
3. I am not currently actively doing support work in my country.

I contacted Grass roots uk who have confirmed the signatories authorised to sign certificates did in fact sign my certificate.

A job description was submitted with my application but removed and handed back to me by a staff member at the visa office. I did not question that as I assumed she knew what she was doing.

I have done support work hence my certificate, and my current situation does not allow me to do support work on a permanent basis. Although I do care for an 88yr old lady in my area, and this is done voluntary.

My question is where did immigration get their information from and was a graphology St used for the signatures.