OP are the shipping bills in your name, or the company's name? If in the company's name, then you needn't worry about your credit rating. (In fact, if the bills are in your name, you can probably resolve this problem quite simply by advising the debt collectors that they should be billing your former company directly...and give them a name and address.)
I'm just saying this because once back in the late 90s I resigned from a job (nicely, gave three weeks' written notice, started the process of searching for my replacement etc.) and the VP of HR was apparently very angry at me for resigning. (Don't know why, but she was, there it is.) Her admin assistant heard the anger and then (in some misguided gesture of loyalty I guess) started forwarding all company correspondence that was addressed to me (pay increase forms, resumes, advertisements, offer letters, confidential employee complaints, invoices, you name it, she sent it) to my home. So maybe this is similar to OP's situation, I dunno. But he shouldn't have to pay the bill.