Rough estimate/quotation

It cannot be proved. You might be wondering if you can prove it through handwriting. 

In very bleak chances you will have to somehow show that you had made the payment through a registered mean. 

Also, has it been endorsed as an estimate? That can also help. 

Regards

Umesh Arora

(Supreme Court of India)

Make an attempt by issuing a legal notice and demanding pacca receipt if only your oral attempts with the jeweler failed already.