I think the CS you spoke to knows nothing about wan ID. You should demand speaking to higher level tech support or report to MCMC for refusing to give you service. Also demand bill rebate for the days of downtime.
By right there is no penalty for not returning the router if you already pass the 2 years contract. You only need to return the BTU because BTU is TM's property.
For Unifi it depends. You could go as low as 30mbps for RM89 or up to 300mbps for RM199 depending on your preference.