If it says free of charge, then it will be so. As I said, I only have the verbal statement from our bank. I cannot look into the contract documents right now because I am not at home.
It definitely used to come with unlimited special repayments. I think around 2017/2018 that changed. When in doubt, ask the bank.
I am a complete beginner when it comes to these subsidies, but as a layperson I think that a change in the repayment terms in 2018 should not affect a loan agreement from 2013. Or am I wrong?