If you owe HMRC anything they should inform you before passing on the debt for recovery. That is you would have received a notice of any tax owed to HMRC. As above call HMRC and establish whether they (HMRC) think you owe them outstanding tax. If yes try to establish who they passed the debt to. Also try to establish with HMRC why there is a discrepancy between your understanding of your tax liabilities and HMRCs understanding of your liabilities.
Recording times and dates of conversations is worthwhile, as is noting the gist of the conversation.
Make a note of every occasion that Rosendales calls – they aren’t allowed to intimidate you and they should not call at unsociable hours.
PS I’m not an accountant so the above in no way constitutes anything other than a personal opinion. I am very opinionated.