ERC Debt Collection Complaint

ERC Debt collection department,

Other (i.e. phone, health club, etc.) Cont'd attempts collect debt not owed Debt was paid Minnesota

A company is attempting to collect debt that I do not owe. There is documented proof that I paid all bills on time ( through - - -. They charged my bank account every month after I sent a check in ( I have bank statements to prove this ) under - account number ( with name, address, phone number ), but they would call me every month saying I did not pay and disconnect my internet. I called them multiple times and complained about this issue and they did nothing to fix it. It was discovered that they had - account numbers under my name ( their mistake, as this was the first and only time I used their service ). Because of this mistaken second account, they are sending me to collections. I paid payments as necessary every month. I should not pay any debt, as there is none. I sent this proof to a collection agency last spring and now I 'm being contacted by another agency regarding the same collection. What can I do? Also, will this harm my credit score? If so, - - needs to fix it, as it is their fault, their mistake.