Unhappy customer

I have joined Debt Buster in April of this year and everything was fine except for one credit provider who is not being included for payment since joining. I keep getting threatening e-mails, messages and calls from this credit provider. The credit provider is included in the contract and I have queried this with Debt Busters a few times and every time I get a response saying they are working on it. How many months does it take to make payment to this credit provider. I have never skipped or paid only a portion to Hyphen PDA. Can this please be resolved as soon as possible.