Hmmmm...tough one. If you think they didn't do a good job, who did you complain to? Is their a Law Society in Singapore which oversees lawyers? Did you contact another lawyer to look through your case?
If there is no feedback from you to your lawyer on how bad a job you think he did, then how is the lawyer to know why you haven't paid his fees?
If the amount the lawyer charged you originally was more than what was agreed up front, do you have correspondence showing this? Is their a written contract between you and the lawyer stipulating how much work he should do and how much he was to charge you? If he's not done the work, or if he's overcharged you, then you are probably within your rights to withhold some of the monies demanded, but again, you have to document this.
If the lawyer has no idea of why you are not paying him, and neither party has contacted the other during this time, then of course the lawyer has the right to ask for the money they think are owed to them. 4 years is a long time, and you have to ask why he's not followed up previously, but still, I'm not sure if there is a time when he no longer can ask.
1: Look through the initial agreement between you and your lawyer.
2: Confirm the costs that you think are reasonable and in line with the agreement.
3: If you have an issue with how your lawyer represented you, find out who (if anyone) governs the working practice of the lawyer and seek redress, possibly with an appeal to your case.
4: Have correspondence with the lawyer, pointing out your reasons for paying a reduced sum/not paying, but make sure you have a leg to stand upon.
5: Once all that is finished, confirm what the lawyer is willing to accept. You may get a reduction, you may get nothing taken off.
6: If you can not pay it all in one go, work out a payment plan and stick to it.
If you keep on ignoring it then they may still come after you and you may end up in court, who may force you to pay.
"Remember that you are an Englishman, and have consequently won first prize in the lottery of life" ...Cecil Rhodes.Poppy Appeal