Repair sloping decking - help!

[Decking321]

I live in a terraced house, on a hill, so the back of the house is lower than the front, and i have a basement kitchen/diner.
When i bought the property my solicitor queried the decking which covers the entire tiny back garden (3mx6mx3m) - it’s small as most of the original garden area is covered by a single storey extension. The decking is level to the house, and touches the bifolds.
The response to the query was that it had been there long enough that planning enforcement would not apply.
Upon moving in, i realised the decking was completely rotten (big holes), so i have replaced the boards with composite and strengthened the existing structure.
One neighbour is complaining about this - saying i need to get planning permission.
I have read all the posts on this but still cant understand.
1. Do i need retrospective PP? If yes, surely i am likely to be granted PP as the footprint of the decking hasnt changed and it has not got higher.
2. My solicitor is not replying to me - what advice do you have re: dealing with this demand from the neighbour? No other neighbours have an issue.
3. Please help!!!

For context - the neighbour seems to believe that the decking has been “extended” - which it hasnt, so i dont understand why it affects him.

 

[Koolpc]

Rubbish...

No need for planning for that.

 

[Decking321]

Rubbish...

No need for planning for that.

Thanks Koolpc that’s reassuring.
I have been so confused with the rules - it covers 100% of garden, probably more than 30cm height (but just continues level from houses, until back fence), so there is no edge per se.
Appreciate your support

 

[big-all]

as long as you just repair damage nothing more your fine
old accepted works are not covered by modern rules and regs as not retrospective

do you have pictures possibly from google earth or old estate agent blurb from previous sales
take dated pictures off pre repair and after repair to show its like for like [all be it more modern materials]

 

[big-all]

and dont under any circumstance apply for anything retrospectively as you now have a structure planning have no say in but as soon as you apply you now have opinions and interpretations and rules applicable now thrown in for no reason