After 10 years service they are terminating my contract whilst I am on maternity leave

I am a self employed dentist in the UK on a NHS contact with the same practice for the past ten years. I am currently 6 months into my maternity leave. I received a letter from my boss last week stating they are terminating my contact with immediate effect due to poor performance over the years. This week I received another letter from them stating they realised they should have given me three months notice, so they are terminating my contract from Feb 2018