The parcel must be containing a legal notice and not summons from a court of law.
These are the tactics and bad practices of collection/recovery agencies of the company.
It is your discretion to accept the cover or not, as the address is wrong. However you may note down the date time phone number of courier from which you received a call. You can comment if required that you had provided the correct address and asked to deliver. Moreover the company always has correct address and they are at fault if they circulate wrong address.
You can lodge a police complaint against this person who shouted and threatened you and obtain complaint number from office of SHO/SSP.
You should have noted down the names, designation, ID card numbers ,of the persons, who came to your residence without taking any prior appointment/ permission from you. You should have asked them to write down the minutes of discussion then and there on the photocopy of their ID card. However although the company collected the true feedback and details and evidences from you in person thru their employees/authorized representative, company failed to deliver solution/resolution/reply to you and did not correct their bill.
Even if the company files a case you can point out the errors and ask them to reverse all overcharged amounts, penalties, late fee, service tax, VAT, surcharge etc and you can demand the charges of phone calls , representations made by you, and subtract it from the bill and issue full and final bill to you, accept their default and issue apology letter, and supply receipt of full and final payment on the spot. You must demand a letter stating that company has not declared you a defaulter to other companies and credit rating agencies and that if they have they shall supply the certified copies of their communications to other companies and credit rating agencies and another letter under original seal and signature of the competent employee of the company stating that they have withdrawn your name from other companies and credit rating agencies.
Be tough with them and make the full and final payment only after they supply all documents.