It could be that revenue thought your income from self employed sources was investment income rather than trading income in which case it is only liable to the 2% health contribution. It appears that if a person with investment income and no trading income has had prsi deducted from paye income they are only liable to the health contribution on investment income.
The following examples from the revenue guide to completing tax returns illustrate:
"Examples to show the liability to PRSI and Health Contributions where an individual has different sources of income are set out below.
Where an individual has employment income that has already suffered PRSI at source, the liability to the Self-Employed (class S) PRSI depends on the type of income the person has.
The following examples will help show the liability to PRSI where an individual has different sources of income.
Example 1
Individual with employment income and no trading income:
Employment income £30,000
Investment income £50,000
PRSI class S liability nil
Health Contribution £50,000 @ 2%
Example 2
Individual with employment income, investment income, and trading income:
Employment income £30,000
Investment income £50,000
Trading income £20,000
PRSI class S liability £70,000 @ 3%
Health Contribution £70,000 @ 2%
Example 3
Individual with employment and trading income:
Employment income £30,000
Trading income £22,000
PRSI Class S liability £22,000 @ 3%
Health Contribution £22,000 @ 2%
Example 4
Individual with investment income:
Investment Income £50,000
PRSI Class S liability £50,000 @ 3%
Health Contribution £50,000 @ 2%
Example 5
Individual with trading and investment income:
Trading income £22,000
Investment income £50,000
PRSI Class S liability £72,000 @ 3%
Health Contribution £72,000 @ 2%
Example 6
Individual with trading income:
Trading Income £22,000
PRSI Class S liability £22,000 @ 3%
Health Contribution £22,000 @ 2%