For something to be proven as defamatory it has to be a lie or untruth.
As long as everything you have said is an honest and factual account of your dealings with the company and it's employees and owners then nothing defamatory (libelous) has been put in print.
If they choose to litigate it may cost them even more.
One would think this is the first salvo in trying to get you to back down.
Good luck and keep up the good fight.
Added: "proven as"