It sounds like an issue with your device then absolutely.
Please take a look at my response from earlier in which I detailed the EE repair process for you under warranty. I also linked the EE websites for repairs and the Store Finder which shows the approximate timelines for repairs being booked in at each store.
The exact process for getting this repaired will depend upon whether you have taken the device on contract or bought this outright from something like the EE Store website.
If the device is on contract with EE, Customer Services will be able to arrange for this to be sent for repair or can book you an appointment for you to visit a local EE store to get this in for repair or sent off (depending on whether they do local repairs or not).
If it was bought outright, the manufacturer warranty will still be valid and you will still be able to take this to an EE Retail store to get sent off under the manufacturer warranty as EE's repair centres are Samsung authorised. Anyone on any network can take a phone to an EE store to be sent off for repair (or locally if they have a repair centre instore/nearby).
They will have a record based on the IMEI that it has already been in for repair once, and hopefully the issue can be reproduced this time. Your only option is escalating it in this way by sending it off, a fault may be found or the repeated escalation may prompt EE to step in.
