Letter from alarm company, England

Hi all, we moved into our property in November 2025. The lady who was selling at the time assured us she had cancelled the alarm contract.

We are receiving letters, albeit addressed to her, that on the envelopes indicate they are demanding immediate payment.

We have not opened the letters so have no clue what the amount is.

We have passed previous letters onto her, and clearly she has taken no action. Any advice on how we should move forward?