What's with the ridiculous funny face?
The OP mentioned that he/she suffered tax of circa €3k in the relevant payslip. That's circa €6k/€7k of extra income in any man's language.
If the other half comes through, it'll be the same story.
It's also unclear whether the €3k of tax was on the extra income or the OP's total income that month!
Given the numbers involved, the idea of engaging a tax professional and undertaking some form of grand exercise could be utterly ridiculous.