Cell c slow internet on full signal

I have a huawei p20 lite dual sim, which has 2 cell c sim cards, one is pre paid and the other is contact. With the pre paid the internet at my house has no problems and showing 4g+. But if i try to use my contact sim for the data sim i only get H with full signal and the internet is so slow it cant even open google. I have gone to the store, i have called, i have even done a sim swop as they suggested it to no avail. I dont recommend using cell c and i have been struggling for months