Can't clean this silver necklace, is it really silver?

[DyslexicPoster]

I bought this sterling necklace of easy. I worn some suncream one day and it turned black. I have since put it in a pandora silver cleaner kit and used a silver cloth, put with tin foil and washing detergent, cleaned with vinegar. It's still quite tarnished. I'm thinking it can't be silver at all? It's starting to look coppery where it did clean up maybe?

.925 is a continental mark for silver showing 925 parts in 1,000 silver.
since 1999 it has become a part of the UK Hallmark - which is a more complex mark, but now includes % of silver - e.g. 925

UK has a hallmarking exemption weight for silver of 7.78 grams (below which it doesn't need to be hallmarked) If above that weight then it is illegal to sell as silver unless hallmarked - it is legal to sell below that weight / to sell continental 'silver' marked only 925

I own (and clean!) a lot of silver jewellery and that’s definitely not silver. To be honest I doubt it was even silver plated, let alone solid 925 silver. That seller is a scamming bastard.

we need to know what shop it is from so we can avoid