Misleading information and sale

My husband phoned Electroparts (Pty) Ltd and ordered a Change over switch to connect the generator power to the main electric board. He was informed to use a SWA 16MM X 3CORE Cable to connect the generator to the power board. The Change over switch as well as the 7 metres cable was delivered but the electrician said its is impossible to fit a three point plug to the cable, and the person who sold is, should have known that it cannot be done. Thus my husband was not advised correctly by Electroparts. If they are professionals, they should have known that it is impossible to use such thick cable for the purposes as explained to them. Now they are trying to find another buyer for the 7 metres cable and do not want to replace it with the correct cable of 6 mm Twin and earth of 6 mm Sufex unless somebody else is prepared to take the 7 metres cable over. Please investigate.