Response times were never agreed
The contract says “support included”. What that means (hours, language, response deadline, escalation) is written nowhere. The vendor delivers what it currently can; the house has no claim, only frustration.
Renegotiate support as a contract item: availability on the house's arrival days, response deadline for a system outage in hours, not days, German-speaking, with an escalation level. In writing. A vendor who will not commit to that should not claim it in the quote either.
