Extremely disappointed with MTM

I have spent literally hours trying to reach MTM on my phone. I cancelled my contract with them in person at their store, then they told me to ring 135. I did so then I received a message that documents were required. I spent 3 hours in their store again yesterday. I later received messages "authentication failed " x 3 and "authentication successful" x 2 times. They took my thumbprints and pulled my records at the store. I have been with them for over 10 years. All payments by debit order. Absolutely terrible service unless one wants to upgrade a contract and get a new phone. I just want to migrate to a lower data contract as I have WiFi at home. Forget ringing them, it is simple a wast of one's time and patience. Very bad service.