Horrible service received at Russells Bochum.

My mom bought a gas stove at Russells, no one informed her that the stove needed to be installed by a qualified technician, she already has an old gas stove so upon delivery my dad disconnected the old stove and connected the new stove, When realising that the stove is not working they contacted the store to request assistance, after almost a month of waiting they are told a they cant help without certificate of compliance by the installer. Why was she not told that the stove needed to be connected by a qualified installer, i believe the sales person should have discussed all these with the customer during the sales transaction,