Hi @hellolc and welcome to the world of business.
I am at a bit of a loss in regards to your post because Direct Credit is initiated by you and a Direct Debit is initiated by the supplier, with your consent.
Leaving that aside, I will offer you some words of wisdom. Avoid giving direct debit authority to any company if you can avoid it and under no circumstances to any telecommunications company. I have run a small business for 14 years and to date the only areas I have had to authorise direct debits for are merchant service fees (Eftpos, Visa and Mastercard) and fuel cards.
I recommend the following methods for paying suppliers:
Within New Zealand
- Direct credit - load them as a bill payee within internet banking
- Credit card
Outside of New Zealand
- Credit card
- Remittance service. I suggest Orbit Remit. Remittance companies are far cheaper then telegraphic transfer (ie: swift) and will generally commit to depositing the full agreed amount without deductions. This is an area I personally recommend to use a option other then a bank.
A handy tip is to pay all the expenses you can by credit card - except where a supplier charges you a premium for this - with a platinum card like the BNZ Business Advantage Visa. 
This offers “cash back” which can give you a effective 1.3% discount on your purchases. Do note if you use this option you will need to include this cash back as “other income” in your financials and pay tax on it. Consult your accountant for specifics.
- BNZ Advantage Visa Business