So long story short -
C sent a message meant for L to you slagging you off saying you were flirting with her husband?
C and L tried to back track or sort the situation by inviting you out for lunch etc probably in the hope you'd stay quiet? But you never engaged
They then left the group probably in disgrace that they were caught out bitching and C would look massively insecure
The others in the group started quizzing and gossiping and once they eventually caught up with C, she said that you were messaging her husband and this is the reason why she sent that message because she believes you were chasing after her husband? But the messages don't exist, it's just a made up story to try and eliminate her looking gossipy and insecure?
Her husband is now backing her up? She's obviously said to him she sent this message to you by accident and to keep up appearances that she isn't a gossiping insecure twat, her husband must go along with this story that you were messaging him trying to get in his pants?
Everyone now believes her because why would she make this up and why would her husband go along with it? She's claiming the messages got deleted?
If this is what has happened, I would get the other 3 together and show them the message that accidentally got sent, the following messages from C and L inviting you for lunch and ask why on earth they would want to get together with you if you had been messaging C's husband? Then I would go round to C's house with someone and say you want to see these messages you apparently sent and ask why on earth she is doing this and if it carries on, you'll be contacting a solicitor about defamation of character and suggest she see's a GP because her behaviour is mentally unstable and she's done all this because she's insecure over her husband talking to someone for a few minutes at her gate and can she seriously sleep at night knowing she's caused you all this trouble then look at her husband and tell him he is just as bad and you won't be lying down and letting them do this to you anymore and you're thinking about actually going to the police so these apparent messages can be recovered