Telephone your insurance company immediately and explain you are completely unaware of any accident. Discuss it with them and try and find out the details. Explain your side of the story. Make a full note of your conversation and who you spoke to. Then follow it up in writing.
I suspect that this is not a scam, but that someone has been in an accident and has taken down the number plate incorrectly. This happens regularly.
It is likely that until this is resolved either through court - at which point you can show it was not you or by the other side realising they have the wrong car, it will be recorded as an "at fault" accident on your insruance, which will effect your premiums. Once it is resolved and you are cleared of fault, your premiums should go down and the excess refunded.