Newsflash: Seller provides receipts, but work isn’t done

Our seller has been remarkably bad about actually completing the items agreed upon in attorney review, but most particularly, they were supposed to have the premises deep cleaned.They provided a receipt that cleaning was done, but the work clearly wasn’t (under a reasonable definition of clean, deep clean, or even according to the list of things provided on the receipt).My question is, who’s liable? Is it the contractor who billed for work not completed, or is it the sellers, who might have even gotten a receipt (due to their relationship with the contractor) without actually having the work done. This same contractor did the remainder of the requested work, some of which was verifiable, some of which wasn’t, but all of which was done poorly.Thanks in advance.