Change of system without notification, we have unused vouchers which cannot be used and no response since April 2017

the unlimited group has changed their double deal system to purchase vouchers. I have 10 vouchers that has not been used and cannot be used as the codes of their vouchers has changed. I have paid for all 10 vouchers in full. Since April i have been contacting the unlimited every 2nd week, and no one cares to respond even thou at the end of every call the promise to get back to me. the last call to them was over 25 minutes. I have been wasting my airtime, my time off work and also the money paid towards the 10 vouchers. This is terrible customer service and we have been with them about 10 years. We cannot even utilise these vouchers . Can someone from management contact me as i am willing to take this further.