I think we need to keep track of separate issues here.
TN-C-S only means that a PEN conductor runs from the DNO transformer to the consumer‘s premises. This PEN is earthed at the transformer and often also along the way (PME). At some point the PEN is split into N and earth conductors. This can be done by connecting both kinds of conductors to one connector or by linking two bus bars.
The PEN can also be bonded to an earth electrode at the consumer‘s premises, which is required by many DNOs, but that’s not a necessary condition for a TN-C-S system.
The questions OP needs to ask a local electrician are
1) Is this a TT or TN supply?
2) If TT, is there a proper earth electrode?
3) If TN, where is the PEN to be split and does it need to be earthed?