Capital Gains Tax Spain

We have recently sold our house in Spain.

We purchased the house with a declared price of E108040 on 4th July 2003. We sold it with a declared price of E242500 on 5th July 2013. We have some invoices that we think we can use to offset some of our tax, but we are still waiting to find out if the information on them is correct. Our purchaser has paid 3% directly to the authorities.

From this information, do you know what our tax bill is likely to be please?

Do people ever refrain from paying the remaining tax and get away with it?

How strict are the authorities about the invoices presented to them to offset the tax. Ours were all sent to us attached to emails, so we are not sure they would be happy to accept them. But, since it was 10 years ago, maybe they would not expect them to be hard copy originals?

I hope you are able to help. Thanks so much.