Unprofessional response, misleading innadequate website, not respecting return law.

Goodmorning to all.
I had been motivited to order a spare part from this website, as it was the most price competitive offer available and presented a top score evaluation.
Nevertheless, upon having ordered the spare on the basis of the car model and engine type of the vehicle data as indicated in the website, it tutned out to be the wrong type of spare part (I had ordered an adblue tank suitable for euro 6.1 and euro 6.2 emissions, whereas the correct type should have been for a euro6.3 emissions type). I reached to this incompatibility conclusion. after attempting to fit the tank to the vehicle in oder to test for proper functioning.
Given the inapropriate type I requested the KFZparts24, to return the wrong item and replace it with the correct type.
KFZparts24 though, refused to accept the return on the basis of additional clauses (not fitting, no liquids) despite the fact that these clauses are against the law and despite the fact that the spare part has NOT been affected at all (since it didn't fit).
On top of that, the company refuses to accept responsibility for misleading the client towards the wrong choise of a spare part on their website and offers a mere symbolic 10% discount to reorder the correct spare part.
Unfortunately I had to refuse their response, since the fundamental problem of misleading to the wrong spare part remains (the site only indicates a warning but DOES NOT provide any alternative choice that could lead to correct spare part.
Another fundamental issue is that it doesn't provide adequate return and refund provision, since it introduces adittional prerequisites (against the law, Return Policy/Widerrufsrecht ).
In conclusion, I am quite dissapointed by kfzparts24 services and I strongly recoment to interested clients to ensure their transactions with the company before proceeding to any contracts with them.