Regarding chargebacks you really need to be careful here. I want you to succeed with it so i'll give you as much info as possible. When and if your credit card company investigates and charge smiths engineering back. Smiths engineering CAN dispute that and actually charge your credit company back. Then your card company can re-chargeback under grounds. So what you need is proof of EVERYTHING. Invoices, discussions, emails. Your mechanic neighbour can help a great deal by being a 3rd party specialist who investigated your engine and established all old parts were used therefore showing smith's didn't carry out what was required. So have your neighbour officially stamp that, and have that ready as proof. Any recorded conversations (or if you can record any conversations) would be of help. With enough proof you should successfully be able to get your money back. But before you do any of that. I would suggest contacting smiths, explaining the situation and what you have found and telling them that unless they fix everything and carried out the work they should have, you will make a claim under the section 75 consumer protection act. Were you have all the proof needed to make the claim and it will incur extra costs on them as well as possibility of brininging their company into disrepute and loosing customers. Record that conversation with them also ;) Best of luck bud, let me know how it goes.