I have been trying to cancel my contract since August however they kept on telling me to contact them after the 14th of September as it will be on month before contract will end but then they try to sell me a data contract in the same breath as to not can

I have been trying to cancel my contract since August however they kept on telling me to contact them after the 14th of September as it will be on month before contract will end but then they try to sell me a data contract in the same breath as to not cancel. However I have been trying since the 14th of September to cancel but the call centre line is not working. They don't respond to emails either. I want to cancel my contract!