There is no point in sending letter after letter to a customer threatening what you will do if you do not receive payment – you need to act on it otherwise they will think you are bluffing.
If you stick to your credit control procedures your customer understands from the start how you work, earning their respect as well as gaining their confidence in your business.
Remember that although you should be firm with your procedures, there may also be times when you need to adjust your approach slightly and be more flexible. Do not sacrifice good working relationships with your clients by being too rigid.
If you say you are going to seek legal advice, then do seek legal advice. It could be the difference of being paid or not getting a penny.