Is Busuu a credited institute?

Can anyone tell me whether it is or not?

I think the short answer is "no". I've just tried looking it up on three websites:

It does not feature on the British Council's list of accredited institutions:
http://www.britishcouncil.org/accreditation-az-list.htm

Nor is it recognised by the British government:
https://www.gov.uk/check-a-university-is-officially-recognised/listed-bodies

Nor is it recognised by the British Accreditation Council - check it out here:
http://www.the-bac.org/accredited-institutions/directory

Don't forget that Busuu does not employ trained teachers: it is a community-based learning forum. Great for what it offers, but still pretty limited in scope. If you need a language qualification, you'll have to look elsewhere.