Nobody can hear me on a call

[Shas1]

So for the last week there has been a fault on a mast nearby so not sure if this is the issue but when I make or receive a call nobody can hear me but I can hear them just fine . But not all the time sometimes it will start working then disappear again . Or one call may be fine and the next not so I have no idea . I have a few bars of signal but surely if it was that I wouldn’t hear them fine or even be able to make the call .

[MI5]

@Shas1 

Difficult to say without knowing the exact mast problem. 
If it doesn't improve or to try anyway, pop in store to get a free sim swap.