Summons as the accused: coordinate the appointment, clarify the allegation first.
You should not ignore a summons as the accused, an unexcused failure to appear can lead to a forced appearance. However, you do not have to make a statement on the matter. From a legal perspective, the right route is to coordinate the appointment through a defence lawyer, to seek file access under Section 51 StPO beforehand or at least to clarify the exact allegation, and only then to decide whether and what to say.
Under Section 49 StPO you have the right to remain silent, the right to a defence lawyer and the right to speak with that lawyer before questioning. A defence lawyer may be present at the interview.