Lancet credit control failure

My mother recently received an unpaid account from Lancet, more than a year after the service date. She queried the account with no feedback. She requested me to help and I queried the account and again, no feedback. Now Lancet handed her over to Debt Collectors, still without ever engaging directly with her except for sending threatening SMS's more than a year after the service was provided. They are not prepared to speak to her to make a payment arrangement and she cannot settle the account in one payment as she is a pensioner with very limited income. They are also not prepared to provide feedback on the question I posed on why it took more than a year to notify her of the outstanding amount and instead of starting the collections process with a phone call, they immediately threatened with handover from the first SMS received.