[1.12.2] Change the amount value (amount of damage) in the LivingAttackEvent event

[NotSoLegacy]

I want to expand the capabilities of one mod. Here is a fragment of his code that interests me:

    @SubscribeEvent(priority = EventPriority.HIGHEST)
    public static void cancelDamageSource(LivingAttackEvent event) {
        EntityLivingBase entity = event.getEntityLiving();
        DamageSource source = event.getSource();

        EntityConfig config = ModConfigs.entityConfigs;

        ResourceLocation entityName = Utils.getEntityName(entity);

        Set<String> sourcesToCancel = new HashSet<>();
        sourcesToCancel.addAll(config.damagesToCancel.get(Pair.of(entityName, null)));

        if (source.getTrueSource() != null) {
            sourcesToCancel.addAll(config.damagesToCancel.get(Pair.of(entityName, Utils.getEntityName(source.getTrueSource()))));
        }

        if (source.getImmediateSource() != null) {
            sourcesToCancel.addAll(config.damagesToCancel.get(Pair.of(entityName, Utils.getEntityName(source.getImmediateSource()))));
        }

        if (sourcesToCancel.contains(source.getDamageType())) {
            event.setCanceled(true);
        }
    }

The result of this block of code is event.setCanceled(true);, meaning the creature will not take damage from the attack. But instead of completely canceling the damage, I want the entity to take more damage.
I thought that immediately after canceling the previous damage event, I could create a new one with an increased damage value. I wrote

	    @SubscribeEvent(priority = EventPriority.HIGHEST)
    	public static void cancelDamageSource(LivingAttackEvent event) {
        EntityLivingBase entity = event.getEntityLiving();
        DamageSource source = event.getSource();
        float amount = event.getAmount();

        EntityConfig config = ModConfigs.entityConfigs;

        ResourceLocation entityName = Utils.getEntityName(entity);

        Set<String> sourcesToCancel = new HashSet<>();
        sourcesToCancel.addAll(config.damagesToCancel.get(Pair.of(entityName, null)));

        if (source.getTrueSource() != null) {
            sourcesToCancel.addAll(config.damagesToCancel.get(Pair.of(entityName, Utils.getEntityName(source.getTrueSource()))));
        }

        if (source.getImmediateSource() != null) {
            sourcesToCancel.addAll(config.damagesToCancel.get(Pair.of(entityName, Utils.getEntityName(source.getImmediateSource()))));
        }

        if (sourcesToCancel.contains(source.getDamageType())) {
            event.setCanceled(true);
            new LivingAttackEvent(entity, source, amount * 7);
        }
    }

But the last line has no effect on the game: the damage is blocked and no new damage is dealt.
What is my mistake and how can I achieve the desired result?

Edited June 10 by NotSoLegacy