Difficulty adding credit to pre pay meter and customer service

I thought the idea of having a smart meter fitted was to make it easier to add credit to your meter without having to go to a paypoint. Every time i try to add credit via the app or on my account online it takes about an hour before they then send me a code about 16 characters long to enter into my home pad…crazy ! Also i paid £200 to add to my credit on March 31st to enable us to have a couple more months at the pre price hike rates. it took them 14 hours to then give me a code which obviously took me into April 1st, NEW RATES !! Now i have written 4 emails, tried to phone numerous times and nothing back, no emails at all since friday. I have not added the credit to my meter as i either want clarification it would be still at the old rate or a complete refund, why should i have paid all that money for them to take 14 hours to add it then charge me the higher rate instead of adding it sooner. NOT HAPPY !