Unless there is some reason to dispute the amount, you should keep up the payments. Whether you pay by cheque, standing order or doorstep collections is up to you. Some of these people add extra charges when they visit your home.
If a debt collector visits your home, you should not invite him inside and, if he is abusive, you should politely ask him to leave.
You may wish to consider visiting your local Citizens Advice Bureau and talking to a debt councillor.