Mrengine contact no ***/4368

Hi please help me with the following issue. I bought a Corolla engine from MrEngine for R16500. and the mechanics fit the engine after that we found that it is faulty. I took it back to show them the faulty equipment. They said I must take out the engine and bring it back to them (which cost me R5000 to take out), when I went to return it they did not have another engine to give to me , so now they want to charge me 10% for returning the faulty engine and promise to refund me 14850 instead of 16 500. This is not right. Until today I have not received my funds back and they have the engine still with them.