Ohhk so first of all, did u give ur exams through the British Council or a school?
Ask ur school or local BC, whichever is ur centre, about these services and how much they cost.
I suggest u first look at the marking schemes of the unit tests u sat for because u might remember wut u wrote wen u hav a look at the marking schemes of ur test papers. They r available here in this site. Just check them and try calculating ur marks. If they are not at all near to wut u got, get a re-check. If u r 100% sure that there has been a mistake, go for it. If not, leave it although it is quite difficult to do so.
There r 2 types of re-check services in my local BC, which is actually my centre.
One is just a Clerical check.
Here they will check if they hav calculated ur grade correcly and taken all ur marks into account and entered ur marks in their system correctly.
Another is a full review.
They will check all ur paper again and then do a Clerical check.
A clerical check costs less than a full review.
There might also be an additional charge of ur centre which will be the administration fee.
You will have to get each module re-checked individually.
If ur module grade changes as a result of the re-check process, u will get ur re-check money back excluding the administration fee of ur centre.
If ur module grade does not change as a result of the re-check process, u will not get any of ur money back.
If u received ur results online, the page that shows ur results has some useful links to the necessary information regarding this.
Hope this helps. All the Best!!