TDU Delivery Charge: TDU stands for transmission and delivery utility — in other words, the utility company in your area that is actually piping the energy from the power generation companies into your home. (Remember, REPs in Texas are just the middleman.) The TDU delivery charge is set by the utility and is consistent from plan to plan and provider to provider within its service areas. For example, AEP , the TDU for Corpus Christi, charges the same delivery fee for all TXU, Direct Energy, and Reliant plans. You don't typically get a choice in utility company, and therefore, these fees are pretty much unavoidable, non-negotiable, and won't factor into choosing an electricity plan or provider.
You should also check your tenancy agreement – but even if your contract bans switching, Ofgem's guidance on this states that if you pay the energy bill, you're still entitled to change supplier any time. You can still compare on Cheap Energy Club if you don't have the former occupants' bills, just hit the "don't know" button when you enter your usage.