Tesco mobile , no service after moving from pay as you go -to pay monthly

CaptainPilotwales

I have been with tesco mobile for many years after my pay monthly contract ended and due to personal reasons I move to a pay as you go sim , after a few years I decided to go back to pay monthly, I took out a new contract using the on line chat and was asure my number would be transferred over to the new  phone after I received it  , I just had to let them know , i should add I had a few days credit on the pay as you go before i changed , I duly received the phone , told tesco ,, and nothing , no service , waited a day went on to the chat , ohh i promise it will be 24 hrs , well 2 weeks later , numerous phone, e mail and chat messages Nothing , last phone call was these things happen , please don't worry we have not lost your number , some lame excuse about  O2 messing it up , need the phone for work and other things just as we all do .
just don't know what else to do , they said if I cancel the contract I lose my number which I have had for over 25 years its on my stationary etc .
any advice  please ?
thanks in advance