Can a collection agency file a lawsuit if they have never sent you a 30 day notice to validate the debt?

Most will since they don't care about the rules, but that would become your defense against them. Failure to validicate te alleged debt.

If you are sued file notice of intend to defend, deny all and demand they produce the original contract you signed, not a copy the original, no contract, no claim.

File complaint with the FTC against them.