refund

What do you say when you want to a complete refund? Can i say

I request you give me a complete refund.???

"I request a complete refund" is fine;
"that you give me" is understood--and indeed, it might have to be a higher up and not the person you address here who finally gives the refund.

But if you really want to have "you" here, go ahead.

"I request that you give me a complete refund" is o.k.;
I prefer the slightly less formal sentence:

"I'd like a complete refund from you."

--C. E. Whitehead

In the UK, at least, "full refund" would be more usual. I agree with C E Whitehead's "I'd like a ..." or "I'd like to request a ..." this is what I would tend to say myself. However, you might be more abrupt if you feel you have been given poor service.