“Ten thousand million” would be the term in “long scale”, traditionally used in Europe (including the UK). In America, we use the “short scale”, so we say “ten billion”. In the long scale, “ten billion” would have an additional three zeroes. I may be wrong, but I believe the tendency nowadays is to use the short scale even in British English. Note that in some cases, the term “ten thousand million” may be used even in the short scale, when convenient (if you want to express everything in millions, for example).

In reports, statistics and other documents containing very large figures such figures are usually given in thousands or millions to avoid writing many zeros.

I have never heard anyone say ten thousand million, mathematically it is correct, but I believe it is almost never used. In any case ten billion is more common and it's easier to say.