@Eliza6826,
Quote:1.Have you received our quotation which we sent you on the 9th July ?
2.Have you received our quotation which we sent it to you on the 9th July ?
Number two is ungrammatical, Eliza.
Have you received our quotation? [which] We sent it to you on the 9th July ?
The relative pronoun, 'which', replaces 'it', when the sentences are joined.
Have you received our quotation which we sent
it to you on the 9th July ?