ᐅ Excavation in Front of Retaining Wall / Support Angle

Hello everyone, I have a question about garden landscaping. In our development area, all plots are on a slope. Our neighbor has built a retaining wall with counterforts (height about 1.50 m (5 feet)) directly on the boundary line to our property and has filled behind the retaining wall to level their land accordingly. The feet of the counterforts extend into the neighbor’s property and are covered with soil to prevent the counterforts from tilting towards our property. This is fine with us; we have no problem with that. Now to my question. I would like to excavate about 1 m (3 feet) in front of the retaining wall on our property and either slope it or build our own retaining wall with counterforts in front to level our land. I understand that this would create a combined embankment about 2.50 m (8 feet) high. We can live with that as the spaces in front of this embankment will be office rooms. Who would be responsible if I excavate up to the boundary on my property and the neighbor’s retaining wall shifts? Would that be my responsibility because I excavated, or would it be the neighbor’s responsibility because the subsoil for their retaining wall/counterforts is no longer stable? I don’t know if this has happened before or if it is just a theoretical concern.