contractor - wrong diagnosis - sending invoice for no work done

[Aariff Kadar]

I had a water leak during rain through a kitchen vent. I had a construction company (i think he is not licensed, never provided his license and nothing available in his invoice) for estimation and received quotation and agreed to start the work. This construction company sub contracted the work to two different companies for two different work. one of the actual licensed contractor came opened my vent and said it is not only fix in the stucco and he said he will send back the construction company. meantime, i had the work done through another contractor because the construction company delayed the call and once when he called i said the work has been taken care and no need of his visit.

now after 2 months he has send me invoice to pay and when i said i will not pay because no work was done and no advice also provided by his sub contractor, he told me he will send it to collections.

what are my options now? can they send it to collections, they have my address and name, how they can impact my credit score? even if they send it to collections, can i tell the collection agency that i don't owe anything.

The amount is less but i don't want to pay for nothing.