just checked the empty bottles and it was definitely X400 they used
You finding empty bottles is not evidence of the chemical that they used, so I would advise you to tread carefully when making your phone call.
i will be on the phone to them tomorrow requesting they come back and do the job right with the correct chemicals.
That isn't a calm or considered approach.
If the company were competent, and if they did use the correct chemicals, what do you think will be the effect of implying to them that they did the job wrong?
You would be better off looking at the product sticker that they've put on your boiler, or cylinder, or in the airing cupboard, or in the loft, to see what they used. If there is no sticker, then look at the invoice to see what they used.
If you can't find any declaration from them of the chemical used, then I would phone them and ask them (a) what they used, and (b) why they did not place a sticker (showing the product and the date of use) somewhere visible.
Resist your temptation to scold, berate or chastise. The more polite you are now, the more it will stand you in good stead later on.
If, at any point, they say that they used anything other than X800,
or an equivalent product of another brand, then tell them, having prepared yourself with some Internet research, why you think that the product they used was not appropriate in the circumstances.
See
here and
here and
here for more information.