Sold car privately - Now buyer want full refund

[McAdam]

Hello,
I am writing here hoping to get a little bit of advice regarding the situation I find myself in.
I sold my car (2011 Vauxhall Corsa) privately on 25th Feb 2020. On the day three gentleman turned up to view the car, they all inspected it and one of them also test drove it giving it the green light and confirmed that the car works and drives well. Even though I was not asked, I mentioned that the timing chain will need changing soon and I also agreed on a £150 discount based on this. We exchanged the V5, completed two AA private car sales contracts, transferred the money and they were on their way.*

After a few days I received a text message asking me for £150 toward the replacement of the timing chain as this was going to cost him £400. I politely declined by saying that I already discounted £150 of the original price and I also informed him of the timing chain even though I was not asked.
After a few more days I receive a phone call from the buyer telling me that he now found out that the car has been in an accident and it also has different engine and he now wants his money back. Again I politely declined and told him that I was not aware of anything like this and that I used the car on a daily basis without having absolutely any issues. This continued for a few days till the point where I had to tell him to only contact me through a solicitor otherwise I was going to report him for harassment. Eventually the text messages and phone calls stopped.
Today,* 7th May 2020 I received a complaint letter from the buyer saying the following: "I now find the goods have been misdescribed. You described the car as covering 48.000 miles from new. When upon inspection we have discovered the car doesn't have the original engine therefore your description of low mileage from new is incorrect".*
He quoted 1979 sale of goods act and asked for a full refund. He also enclosed in the letter a copy of my advert and a copy of the engine number (photo of an engraved metal plate that is unreadable) and claims that it doesn't match the V5 information.

A few relevant facts:
1.I owned the car for 8 months and bought it with a one year MOT valid from 12th June 2019 to 11th June 2020.
2. I have a HPI check that I made before buying the car on 20th June 2019 and an invoice for the purchase that follows on the next day 21st June 2019.
3. We both signed an AA private car sale contract in which is stated "sold as seen"
Happy to provide any additional information if needed.
Thanks in advance
*

[des8]

It was a private sale
He saw the vehicle and examined it prior to purchase
The vehicle could well have a low mileage at 48,000 miles, even if the engine was replaced so I don't understand his complaint.
Anyway caveat emptor applies.

[MIKE770]

Anyway caveat emptor applies. = buyer beware

[McAdam]

A friend of mine told me that he might replace the engine himself considering that is was quite low mileage and he now tries to scam me into giving him a refund and be stuck with a tampered car

I`ve also been at the Citizen Advice to seek some guidance and they told me that he hasn't got a case against me.
All this situation has started affecting me because I tend to overthink stuff and stress quite easily.

Would there be anything I could do in case he doesn't stop contacting me?

[MIKE770]

solicitors letter?
*

[des8]

Write (send letter with free certificate of posting from post office) warning him to stop and tell him that if he doesn't you will consider it as harassment and report him to the police for an offence under the Protection from Harassment Act 1997?