Unfriendly sales lady and manager

My husband and I bought 2 boot shocks for our car, only to find that we needed 1. When we took them back to Renault (Motus Isuzu Bloemfontein) unfortunately they couldn’t help us. Apparently it was a special order and they can’t take it back, there was no ‘No Return Policy’ clause on their invoice, even though they wrote that they charge a 10% handling fee for all returns ours wasn’t even looked into. The sales lady is rude and the manager is even worse, he doesn’t even try to make means...We feel unfairly treated.