MSE energy switch - can you switch from BG to BG and still get cashback/boiler cover?

I was with Centrica for years for boiler cover but their prices kept going up and up and they wanted £28 from me and that was after contacting them to negotiate a better price. In the end I cancelled the boiler cover so effectively was no longer a customer. Two months down the line I went with British gas through the energy site here expecting to receive the free cover. A day before my energy went live with BG I received a letter to say I was still a customer so could not have the energy cover. I contacted them to inquire about this and they agreed I was no longer a customer, but, you could not have or renew the cover unless 3 months had passed from the time you were a customer to when you sign up again. I could not fined this information anywhere when I applied for energy . On the Martin Lewis site it just states for new customer only. Couldn't find this 3 months rule anywhere on site. Iunderstand this but I was angered to receive a letter to say I was still a customer so put in a complaint which was dealt with quickly and effectively. Upshot was they gave me the boiler cover so a good outcome but I find the excess fees calling out an engineer rather high so not sure whether I will use it or not. It will depend I suppose on how well my heating system works. Also no free annual boiler check. They are quoting £60 upwards for that! So is the cover really worth it I wonder.