Not getting Bandwidth for which I am paying.

Since signing on for a 20MB fibre line with Mweb in October 2019, I have experienced intermittent bandwidth of below 5 MB/s, occasionally dropping below 1MB/s.

Although MWeb support has attempted to resolve this matter since November 2019, I am arguing that I am not getting the service for which I am paying. I want to cancel the contract, however I am told I will be responsible for penalties for cancelling the contract early.