Unfair handover

I was contacted last year for a data sym contract telephonically. I agreed for the deal it was 200 a month for 40gig data day and night. I never received contract. From the beginnig O had problem with connections and they deducted two months on the 8th of the month while we agreed on he last day of the month for debit order. After the third deduction they did not deduct again. I was never contacted and I did not have ths number of the devision that contacted me. I went to the local office ones they said that I must contact that people. I waited to hear from them only for them to contact me last month saying I was handed over and now I have to pay 2900. I told the lady I am willing to pay the money for data used and it was there mistake. I aas never contacted about overdue account by them. I feel unfearly treated