I have a question, I signed a rental agreement with a management company and was just informed that that management company has now become different

While you question references signing a rental agreement with a management company, many leases are between Landlord and Tenant, with the management company just acting as agent for the Landlord.  If this is the case, the change of the management company managing the property for the Landlord has no effect on the Agreement between Landlord and Tenant and would not make the lease agreement null and void. As to the plumbing issue, if you are having communications with the landlord directly, you can communicate your issues and problems with the plumbing (as well as the management company) to the Landlord.