Information regarding reclaiming Dividend Witholding Tax via Foreign Tax Credit relief claim

Hello I have been charged a Dividend Witholding tax on dividends I've received from stock holding in a South African Company. After research it appears my options to reclaim this tax are either by attempting to retrieve a refund through the South African Government which would entail several forms and records or through a Foreign Tax Credit relief claim with HMRC which is my preferred option. As the stock holdings are within an ISA, does anyone know if this refund can be returned to the ISA without impacting the ISA contribution limits? My logic being that this money would have been within the ISA wrapper had the correct tax been applied so it feels reasonable for this money to be allowed to be put back into the ISA wrapper without counting towards the ISA contribution allowance. Also can somebody advise if I can claim for the full amount that I paid as Witholding Tax, in this case 20%, or can I just claim for the difference between that amount and the lower amount that would have been applied in accordance to the Double Taxation Agreement between the UK and South Africa had that been applied correctly, which I understand to be 10% as per this link https://www.gov.uk/hmrc-internal-manuals/double-taxation-relief/dt17353 I would greatly appreciate if someone far more knowledgeable than myself could confirm that I've interpreted that correctly. I am a UK resident and Private Investor for clarity. Many thanks in advance for any help you can provide

Hi,

You can claim for the full amount of withholding tax in the foreign section of a Self Assessment tax return.  

If HMRC repay the tax via a foreign tax credit, then this cannot go into the ISA, without contributing to your £20000 limit.

Thank you.