Ok first have you cased the leather, some leathers are very hard and that said yours could be one of those. But that being said most all veg tan can be tooled. Wet (dampen) the leather with a clean sponge and distilled water (if you have distilled) if not tap water will work. Wait till the leather just starts to return to its normal color then try tooling it. Here is the start, you didn't say water you did to start you may have already followed these steps. Veg tan for a belt should be 6 oz. to normally 10oz sorry I do not have my metric chart with me, so it should be thick. Repost here and let people know what you have done and any pictures maybe worth thousands of words.