Property isn't vacant, or the seller's left stuff behind?
First of all, call your solicitor and send them pictures of the items. The solicitor will inform the seller's solicitor to come and collect their items. Don't throw any of the items away or cause damage to them. Store them safely until the seller comes to collect them - most likely, it is an honest mistake.
If the seller refuses to collect the items, then you should speak to your solicitor about starting legal proceedings to get the items removed. Always act reasonably and do not damage the items.
Andrew Boast FMAAT MIC is co-founder of SAM Conveyancing.