Bullying of client

We received an Notice of demand from the above Company for Municipal rates.We then contact the municipality where they gave us the instructions to pay them.Nudebt then refuse to accept this payment and demand us to pay the money to them. After making an offer they reuse to accept my offer saying the consequences will be non payment. They insist on their own payment amount of 2 payments however i cannot afford to pay this into 2 payments. According to law a creditor cannot refuse to acceot an offer and also cannot bully you.