company offered free consulation now want money

I had a free consultation with a marketing company. I ended up rejecting them and working with a different company. The rejected company went to my website (i have an online business) and decided that I implemented some of the ideas that the gave me in the free consultation and therefore they want $150 consultation fee. The emailed me an invoice. I send them and email back that we feel that we don't owe then a thing. In fact the ideas that they claim we took from the consultation were brought up by the new marketing company that we hired. Can someone just randomly produce an invoice? what should i do? can they take me to collection? I did not sign anything. and the consultation was free? I assume they will use it as bad debt when they file taxes, but they will get a deduction for money no one owed them, should we inform the IRS? I would not want to do it to anybody, but I don't want my company to show up and not paying debt.
Please help,
thanks,
Alex

They absolutely cannot do that. A consultation is just that and you need not pay unless you agreed.