Same here . I thought the cap would be R7 ...but I don't know what an R11 cap is to be honest .
Just found an R11 cap lamp ..............looks the same as an R7 to me .
Why don't you take the lamp with you to a wholesaler , it'll be correct then .
Whatever you do , make sure the fitting is switched off .....halogen linear tubes can reach 300 deg. C ...you didn't want to be touching it .