Bad cell reception - always

The reception that I get with my cellphone network is shocking. I am with Cell C. I upgraded in January so the phone itself is new and there is nothing wrong with it so that cannot be the problem. Whenever I am in an area with friends and family on other networks like Vodacom and MTN, they have perfect cellphone reception and can call, whatsapp etc with no issues. My reception is bad no matter where I am. Whatsapps are forever hanging and taking long to go through. Phone calls are a nightmare as I catch every fourth word the other person is saying and they can barely hear me. I cannot have a decent conversation and the frustration that goes along with it is UNACCEPTABLE as I pay a lot every month to have a contract with Cell C. This has been going on for a long time - long before I upgraded so the brand of phone or any other factor has nothing to do with it.