There is a callback request form on the website here.

They are based in Merlin House, which is a full or part serviced office space by Asmec. See here. The main number for the building is given as 0118 9026400 and a search of 192.com for other businesses at that post code, reveals they all have 0118 9026xxx numbers. Asmec will most probably provide the telephone facilities which all have similar DDI numbers. Going by what I've just seen on 192.com I would say that they are 0118 9026400 through to 0118 9026999. As for which belongs to Fujin, well if it's not been posted anywhere on the internet, then we're not going to find it.

You could try 0118 9026400 and ask to be put through or ask what the extension is for Fujin Technology. If you have the extension number, then you can put it onto the end of the 0118 prefix.