Overpaid by work - what to do?

[Smarshian]

I started a new job in December and my pay has not been correct from the off.
The job was advertised as f/t but I negotiated 0.9 (36 hours) over 4 days. We discussed salary and agreed on a number. In my first full month I received the f/t salary (not 0.9). I informed my boss about this and said obviously I’m happy to take the extra but it’s not as agreed. She said she would sort it but I wouldn’t lose all the extra. I was then paid the same for Feb and March, nothing has been mentioned to me since.
Annual pay reviews usually happen in April, but haven’t had 1:1 due to COVID. I wasn’t expecting much due to being there for a short time, however I’ve just received my payslip and I’ve had a 25% payrise on top of the original overpayment 🤯.
What do I do?

I would put the amount you've been overpaid into a separate account and not spend it until you've got this sorted with work. Just in case you end up needing to pay it back

Email your boss and HR (make sure everything is documented) to make them aware of the overpayment, if nothing is still done then I would keep that money aside to cover the next few months if/when they rectify it. As long as you keep telling them and it’s all documented then that’s all you can do.

Could the pay rise be correct? I would query this in the same email and ask them to confirming exactly what the pay rise is.

Agreed with Wife.

Someone will do a reconciliation at some point and ask for it back.

So put it somewhere, let it earn interest. Or put it into premium bonds if you could get it back out again with enough haste to pay them back, that way at least you have a chance of winning big from it.

They will ask for it back eventually. I was overpaid by a substantial amount during mat leave (i didnt know as they had given me the wrong figures so i thought it was right) i was then hit with a big bill at the end when i had no money.

Put it aside as others have said and contact hr to move it along